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?

We'll use their second letter.

h = 3o

e = o - 13

h + e + o = 72

Solve for o.

We substitute the first two equations into the last equation:

3o + (o - 13) + o = 72

5o - 13 = 72

5o = 85

o = 85/5 = 17

Answer: 17

Let's check we get h=3o=51, e=o-13=4 and we check 17+51+4=72, good