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
