Mark hires a singer for 3 hours at $15 an hour.  He then tips the singer 20%.  How much did he pay?
The cost was 15*3=$<T>multiply(15, 3)=45
So the tip was 45*.2=$<T>multiply(45, 0.2)=9.0
So in total, he paid 45+9=$<T>add(45, 9)=54
