John decides to learn how to play the piano.  He buys a piano for $500.  He then hires a teacher for 20 lessons at $40 per lesson but ends up getting a 25% discount.  How much did everything cost?
The normal price of the lessons would be 20*40=$<T>multiply(20, 40)=800
The discount saves him 800*.25=$<T>multiply(800, 0.25)=200.0
So the lessons cost him 800-200=$<T>subtract(800, 200)=600
That means everything costs 500+600=$<T>add(500, 600)=1100
