Answer:
A. 3
Explanation:
Fist, we need to figure out how many students said "dogs" and how many said "cats".
30% of 40 is...
40 x .30 = 12.
12 people said dogs.
22.5% of 40 is...
40 x .225 = 9
9 people said cats.
If 12 people said dogs, and 9 people said cats, then 3 more people said dogs than cats.