How can I extract this method and have it the same name?

I am creating a mortgage calculator, and I'm following a tutorial. I want to extract a method and name it getMonthlyInterest, because there were two instances of a method, and the tutorial originally is able to use getMonthlyInterest for both.

开发者_开发知识库annualInterest / PERCENT / MONTHS_IN_YEAR

This code was replaced by "getMonthlyInterest" I typed this a second time:

private float getMonthlyInterest() {
        return annualInterest / PERCENT / MONTHS_IN_YEAR;
    }

and the software did not allow me to name the float "getMonthlyInterest," saying that the name "getMonthlyInterest" was already used. I want to use "getMonthlyInterest" for both of them, how can I do that?

Whole Code of Class:

public class MortgageCalculator {
    public final static byte MONTHS_IN_YEAR = 12;
    public final static byte PERCENT = 100;

    private int principal;
    private float annualInterest;
    private byte years;

    public MortgageCalculator(int principal, float annualInterest, byte years) {
        this.principal = principal;
        this.annualInterest = annualInterest;
        this.years = years;
    }

    public double calculateBalance(short numberOfPaymentsMade) {
        float monthlyInterest = getMonthlyInterest();
        float numberOfPayments = years * MONTHS_IN_YEAR;

        double balance = principal
                * (Math.pow(1 + monthlyInterest, numberOfPayments) - Math.pow(1 + monthlyInterest, numberOfPaymentsMade))
                / (Math.pow(1 + monthlyInterest, numberOfPayments) - 1);

        return balance;
    }

    private float getMonthlyInterest() {
        return annualInterest / PERCENT / MONTHS_IN_YEAR;
    }

    public double calculateMortgage() {

        float monthlyInterest = getMonthlyInterest();
        float numberOfPayments = years * MONTHS_IN_YEAR;

        double mortgage = principal *
                (monthlyInterest * Math.pow(1 + monthlyInterest, numberOfPayments))
                / (Math.pow(1 + monthlyInterest, numberOfPayments) - 1);

        return mortgage;
    }

    private float getMonthlyInterest() {
        return annualInterest / PERCENT / MONTHS_IN_YEAR;
    }

    public short getYears() {
        return years;
    }
}