Question 616757
There will be no time in the future that you would be three times his age. However using x as his age you can use the formula:

3x = x + 21

(as you are 21 years older and would be three times his age at the same time. So you can then find out his age at the time (x)

3x - x = 21
2x = 21
x = 10.5

So he would be 10.5 and you would be 31.5