In 5 years, Joey will be as old as Beth is now. If Joey is 9 now, how old was Joey when Beth was Joey's age now?
Beth is 5+9=<T>add(5, 9)=14 now.
Beth was 9 years old 14-9=<T>subtract(14, 9)=5 years ago.
Joey was 9-5=<T>subtract(9, 5)=4
