9 years from now, John will be 3 times as old as he was 11 years ago. How old is he now?
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 = 
<gadget id="calculator">42/2</gadget>
<output>21</output>
21.

<result>21</result>