Answer:
see explaination 
Explanation:
SavingsAccount.h
#pragma once
#ifndef SAVINGS_H
#define SAVINGS_H
//SavingsAccount class declaration
class SavingsAccount
{
 //declare data members
private:
 //set annualInterestRate to 0.0 default value
 static double annualInterestRate;
 double savingsBalance;
public:
 //set the balance
 void setBalance(double);
 //modify interest rates
 static void modifyInterestRate(double);
 //retruns total balance with interest
 double calculateMonthInt();
};
#endif
SavingsAccount.cpp
//include required header files
#include<iostream>
#include"SavingsAccount.h"
using namespace std;
//set the annualInterestRate to 0
double SavingsAccount::annualInterestRate = 0;
//static funtion modify interest rate
void SavingsAccount::modifyInterestRate(double iRate)
{
 annualInterestRate = iRate;
}
//set the balance
void SavingsAccount::setBalance(double bal)
{
 savingsBalance = bal;
}
//calculating savings balance with monthly interest
double SavingsAccount::calculateMonthInt()
{
 double monthInt = 0;
 monthInt += savingsBalance*annualInterestRate / 12;
 return savingsBalance += monthInt;
}
DriverProgram.cpp
//include required header files
#include<iostream>
#include "SavingsAccount.h"
using namespace std;
//main methods
int main()
{
 //delcare class objects
 SavingsAccount saver1, saver2;
 
 //setter functions of balance
 saver1.setBalance(2000.00);
  saver2.setBalance(3000.00);
 //Setting annual interset 0.03 to static variable
 saver1.modifyInterestRate(0.03);
 //finding the balance in saver1 and saver2 account
 cout << "Balance of saver1 and saver2 on 3% interest Rate\n";
 cout << "--------------------------------------------------\n";
 cout << "Balance of saver1 = " << saver1.calculateMonthInt()
 << endl;
 cout << "Balance of saver2 = " << saver2.calculateMonthInt()
 << endl << endl;
 //Setting annual interset 0.04 to static variable
 saver1.modifyInterestRate(0.04);
 cout << "Balance of saver1 and saver2 on 4% interest Rate\n";
 cout << "---------------------------------------------------\n";
 cout << "New Balance of saver1 = " << saver1.calculateMonthInt() << endl;
 cout << "New Balance of saver2 = " << saver2.calculateMonthInt() << endl<<endl;
 return 0;
}