Question

When I was 14 years old, my father was 3 times my age. Now he is twice my age. How old am I?

Answer 1

When he was 14 his dad was 42
now the child is twice 14... = 28...

Answer 2

Let f be the father's age and his child's age be c.

As the father is 42  14 = 28 years older than the child, f = c + 28.

At the moment f = 2c, hence 2c = c + 28, and so c = 28. That is, the father's child is now 28 years old.