8 years ago James was twice Janet's age.  In 15 years James will turn 37.  Susan was born when Janet turned 3.  How old will Susan turn in 5 years?
James is 37-15=<T>subtract(37, 15)=22 years old
So 8 years ago he was 22-8=<T>subtract(22, 8)=14 years old
That means Janet was 14/2=<T>divide(14, 2)=7.0 years old 8 years ago
So Janet is now 7+8=<T>add(7, 8)=15 years old
That means Susan is 15-3=<T>subtract(15, 3)=12 years old
So in 5 years she will be 12+5=<T>add(12, 5)=17 years old
