Maths問題

Given : Mary is X years old, and Tom is 4 years older than her, so Tom’s age
= X+4
Since their father is 3 times as old as Tom. Now, let his age is Y. Then,
Y = 3*(X+4)
=3X+12
Therefore, their father is (3X+12) years old.

Mary's age = X
Tom's age = 4+X
∴their father's age = 3(4+ X)
ˉˉˉˉˉˉˉˉˉ=12+3X