Explanation:
x = Aly's age
y = her mother's age
x + y = 52
x = y/3
we simply use the identity of the second equation in the first equation :
y/3 + y = 52
y + 3y = 156
4y = 156
y = 39
x = y/3 = 39/3 = 13
Aly is 13 years old.
her mother is 39 years old.