Thomas is three times as old as Toby. Terrence is 13 years younger than Toby. The sum of the ages of Thomas, Terrence and Toby is 72. How old is Toby?
T=Toby's age
THomas=3T
Terrence=T-13
T+3T+T-13=72
5T-13=72
5T=85
T=17
Toby is 17 years old.
+539 
