Haha I basically stumbled upon my answer as I was trying to figure out what the right equation is 

That's correct, but again there is an equation to be found and solved :)

There are two points in time, now and then.

We define $$x$$ as Jimmy's age now.
"Then" is when Tom was $$x$$ years old.

| Person | Now | Then |
| ----- | ----- | ----- |
| Tom | 24 | x |
| Jimmy | x | |

To get from now to then (reading Tom's line) we subtract 24 and add x, hence the bottom right cell is $$x-24+x = 2x-24$$.


| Person | Now | Then |
| ----- | ----- | ----- |
| Tom | 24 | x |
| Jimmy | x | 2x-24 |

Now the equation is simply $$2 \times (2x - 24) = 24$$, or $$x = 18$$.


Scroogey

science

Secondary school math puzzle

Jimmy was 12 when Tom was as old as Jimmy is now.

Thus, Jimmy is 18 now, because 6 years ago Jimmy was 12 and Tom was 18.

I did guess and check again, haha.
