One-third of Olivia’s age, increased by 12, is equal to twice her age, decreased by 3. How old is Olivia?

Answer 1

Just translate the sentence into Math:
let Olivia's age be x

One-third of Olivia’s age, increased by 12:
(1/3)x + 12
is equal to : =

twice her age, decreased by 3:
2x - 3

put it together, then solve:
(1/3)x + 12 = 3x - 3

I suggest multiplying each term by 3 to get rid of the fraction

Answer 2

25