Well, there are 12 inches in a foot.
We have 3/12 inches (3 inches of a foot). Now, let's simplify!
What is the GCF (greatest common factor) of 12 and 3? Well, let's list out the factors (what a number divides into) of each of them.
1*12
2*6
3*4
1*3
The largest factor that we see in both of these numbers is 3, so let's divide 3/12 by 3!
3/3=1
12/3=4
So, 3 inches are 1/4 of a foot :).
You can check your answer by multiplying 12 by 1/4. Your answer will be 3!
I hope I helped! :)