Answer:
D.
Explanation:
Clyde's present age is 7+8, because he has aged 8 years since he was 7.
So, the equation would be C=7+8.
However, that equation isn't listed so you need to move some numbers around.
If you subtract 8 from both sides of the equation C=7+8, you get C-8=7, which is D.
Hope this helps! :)