James needs to get a new pair of glasses.  His frames cost $200 and the lenses cost $500.  Insurance will cover 80% of the cost of lenses and he has a $50 off coupon for frames.  How much does everything cost?
He gets 500*.8=$<T>multiply(500, 0.8)=400.0 off the cost of lenses
That means the lenses cost 500-400=$<T>subtract(500, 400)=100
The frames cost 200-50=$<T>subtract(200, 50)=150
So he pays 100+150=$<T>add(100, 150)=250
