Question 1003224
Call their ages NOW, s and m.  Then we have
s - 4 = 3(m - 4)
s + 20 = 2(m + 10)
We can simplify these and get
s - 4 = 3m - 12
s = 3m - 8
and
s + 20 = 2m + 20
s = 2m
Since they both equal s, set them equal to find m.
3m - 8 = 2m
m = 8 years old