解;设X年后爸爸的年龄是儿子的3倍.
(37+X)÷3=9+X
37+X =9 +X×3
37+X =9+3X
37+X-3X =9
37-3X = 9-X
3X+X =37-9
4X = 28
X =28÷4
X =7
7年后