Hi there!
Okay, so this is pretty simple. Just follow my instructions!
1/4a = 3
4 * (1/4a) = (4) * (3)
Use a calculator to solve this, remembering PEMDAS.
a = 12
Your final answer is a = 12. When in doubt replace "a" with the new given variable number, which is twelve.
Hope this helps!
And by the way, I love the attached file. It's really cute! :P