A real estate office handles 50 apartment units. When the rent is $600 per month, all the units are fully occupied. However, for each $40 increase in rent, one unit becomes vacant. Each occupies unit requires an average of $27 per month for maintenance. Write a program that prompts the user to enter the number of apartment units, the rent to occupy all the units, the increase in rent that result in a vacant unit, amount to maintain a rented unit. The program then outputs the number of units to be rented to maximize the profit.