Answer:
9 years ago.
Explanation:
Dotty is 51 years old and Esmerelda is 23 now.
Now, x years ago the age of Dotty was (51 - x) years and the age of Esmerelda was (23 - x) years.
Assume that x years ago Dotty was 3 times Esmerelda's age.
So, we can write the equation as
3(23 - x) = 51 - x
⇒ 69 - 3x = 51 - x
⇒ 69 - 51 = 3x - x
⇒ 18 = 2x
⇒ x = 9 years.
Therefore, 9 years ago Dotty was 3 times Esmerelda's age. (Answer)