Use reasoning to answer the following question.
9 years from now, John will be 3 times as old as he was 11 years ago. How old is he now?

21
Let J represent John’s age.

We have J + 9 = 3(j − 11).

So, J + 9 = 3J − 33.

So, 9 = 2J − 33.

So, 42 = 2J.

Which means that John’s age is J = 42 / 2 = 21.

.

Thus, the answer is 21