Question

Is this answer correct? Thank you

Answer 1

Pretty much, but since it asks what the ratio of puppies to kittens is, I'd write it as 12:36.

You should also simplify it, to a 1:3 ratio.

Answer 2

Your answer is technically correct, but you need to simplify it. Both 12 and 36 can be divided by 12. After doing that you get:
1:3
Also, you need to make sure the order is correct, 1:3 also fixes the order.