John buys 30 ducks for $10 each.  They weigh 4 pounds and he sells them for $5 per pound.  How much profit did he make?
He bought the ducks for 30*10=$<T>multiply(30, 10)=300
He sold each duck for 4*5=$<T>multiply(4, 5)=20
So he sold all the ducks for 30*20=$<T>multiply(30, 20)=600
So he made a profit of 600-300=$<T>subtract(600, 300)=300
