I need help with this one...at the bottom is what I have done so far.

If P is the population on the first day of the year, B is the birth rate,
and D is the death rate, the estimated population at the end of the year
is given by the formula:
P + B*P - D*P
100 100

The population growth rate is given by the formula:
B-D

a. growthRate: this method takes as its parameters the birth and death rates,
and it returns the population growth rate.

b. estimatedPopulation: this method takes as its parameters the current population,
population growth rate, and n, the number of years. It returns the
estimated population after n years.

Your program should not accept a negative birth rate, negative death rate,
or a population less than 2.
------------------------------------------------------------------------
import java.io.*;

public class birthandDeath
{
static BufferedReader keyboard =
new BufferedReader(new InputStreamReader(System.in));

public static void main(String[] args) throws IOException
{
int startP, birth, death, years;

System.out.println("Enter the starting population: ");
System.out.flush();
startP = Integer.parseInt(keyboard.readLine());
System.out.println("Enter the birth rate: ");
System.out.flush();
birth = Integer.parseInt(keyboard.readLine());
System.out.println("Enter the death rate: ");
System.out.flush();
death = Integer.parseInt(keyboard.readLine());
System.out.println("Enter the number of years: ");
System.out.flush();
years = Integer.parseInt(keyboard.readLine());
}