Verified Answer :

30, multiply 4 by 2.5 to get 10, then multiply 12 by 2.5 to get 30 (or x).

Hi Brainiac

4/12 = 10/x
Use cross multiply
4x = 120
Divide both sides by 4
4x/4 = 120/4
X = 30

The answer is A

I hope that's help :)