Answer:
A: 8^2+y^2=12^2
Explanation:
pythagorean theorom is a^2+b^2=c^2
the legs are a and b and c is the hypothenuese
we know a is 8 and c is 12 so lets fill it in
8^2+b^2=12^2
b side is known as "y" so let's replace b with y
8^2+y^2=12^2
and this matches answer option A
Hopes this helps