9 years from now, John will be 3 times as old as he was 11 years ago. How old is he now? Give me reasons, before answering the question
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. So the final answer is 21.