John sublets his apartment to 3 people who each pay $400 per month.  He rents the apartment for $900 a month.  How much profit does he make in a year?
He gets 3*$400=$<T>multiply(3, 400)=1200 per month
So he gets 1200*12=$<T>multiply(1200, 12)=14400 per year
So he pays 12*900=$<T>multiply(12, 900)=10800 a year
That means his profit is 14400-10800=$<T>subtract(14400, 10800)=3600 per year
