PLEASE HELP!! with this java problem...

Question

Ok so I have this assignment regarding Loan calculations: Compute the Monthly Payments given> the APR, #of payments, and amount borrowed. The formula for this is...P= Cr(1+r)^N / (1+r)^N -1 Where P is aount payable each month, r is APR which needs to be converted into months by /12, N is number of payments, and C is total amount owed. I got this:
import java.lang.Math;
import java.util.Scanner;
public class ComputeSomething
public static void main (String s[])
//obtain input from the user
//validate input
//proceed if input is valid
//process input
//repeat the above four steps until "quit"
Scanner input = new Scanner (System.in);
double payable_amount; // P
double amount_owed; //C
int number_of_payments; //N
double rate; //r
double numerator, denominator;
System.out.print("Enter the value of amount borrowed/owed: ");
amount_owed = input.nextDouble ();
System.out.println ();
System.out.print ("Enter the value of number of payments: ");
number_of_payments = input.nextInt ();
System.out.println ();
System.out.print ("Enter the value of rate as a percentage, e.g., 10 for 10%: ");
rate = input.nextDouble ();
System.out.println ();
rate = rate/(100*12) ;
numerator = amount_owed * rate * Math.pow ((1+rate),number_of_payments);
denominator = Math.pow ((1+rate),number_of_payments) - 1;
payable_amount = numerator/denominator;
System.out.println("The amount payable per month = " + payable_amount);
// // implement the second formula
// numerator = Math.log (payable_amount/amount_owed) - Math.log ((payable_amount/amount_owed) - rate);
// denominator = Math.log (1+rate);
// number_of_payments = (int)Math.round (numerator/denominator);
NOW I have to change it around for the second formula and this is where I am lost cause it has logarithms....This formula goes like this N= ln P/C - ln (P/C-r) / ln(1+r) Where N is the number of monthly payments, C is the sum of actual amount borrowed which is given and r is APR, and P is the monthly payment and ln is the natural logarithm. SO in this formula I have to calculate the NUMBER of payments given the other input.... This project is just a simple command line format so the user just types in the inputs. ALSO there needs to be a command to end the session and the program needs to handle incorrect input too!!
**I dont know how to do the second formula PLEASE HELP ME.....the formulas in picture format are located at http://www.efunda.com/formulae/finance/loan_calculator.cfm**

Answer 1

Oh man sorry..what I mean to say is that yes it is a command line type program (no menus) and its going to be in the following format: you type 1 for calculating monthly payments, type 2 for #of payments, and then type 0 to quit. When you type 1 or 2 then the correct formula for each option will then be utilized by asking the input for the fields kinda like this program for a simple fahrenheit to celsius conversion:
import java.util.Scanner;
public class TempConverter
// solution to inclass assignment
public static void main (String s[])
double temp_in_celsius;
double temp_in_fahrenheit;
Scanner input = new Scanner (System.in); // create a connection 'object' to read data from the k/b
// create the menu that is displayed to the user
System.out.println ("Choose 1 to convert temp. from C to F, 2 to convert temp. from F to C and any other value to quit");
int choice = 0;
if (input.hasNextInt ())
System.out.println ("correct data type");
choice = input.nextInt ();
else
System.out.println ("incorrect data entered -- program terminated!");
System.exit (0);
// while choice is either one or two, continue; quit otherwise.
while(choice == 1 || choice == 2)
if (choice == 1)
//code for converting temp from C to F
System.out.println ("Enter the value of temp. in the C scale: " );
if (input.hasNextDouble ())
temp_in_celsius = input.nextDouble ();
temp_in_fahrenheit = ( (9/5.0) * temp_in_celsius ) + 32;
System.out.println ( temp_in_celsius + " in degrees C is " + temp_in_fahrenheit + " in degrees F");
else
System.out.println ("incorrect data entered -- program terminated!");
System.exit (0);
else if (choice == 2)
//code for converting temp from F to C
System.out.println ("Enter the value of temp. in the F scale: " );
if (input.hasNextDouble ())
temp_in_fahrenheit = input.nextDouble ();
temp_in_celsius = (5/9.0) * (temp_in_fahrenheit-32); //convert the temp to the C scale
System.out.println (temp_in_fahrenheit + " in degrees F is " temp_in_celsius " in degrees C");
else
System.out.println ("incorrect data entered -- program terminated!");
System.exit (0);
else
System.out.println ("Quitting");
System.out.println ("Choose 1 to convert temp. from C to F, 2 to convert temp. from F to C and any other value to quit");
if (input.hasNextInt ())
System.out.println ("correct data type");
choice = input.nextInt ();
else
System.out.println ("incorrect data entered -- program terminated!");
System.exit (0);
}