You want to isolate the variable 'y'.

Subtract 10 to both sides:

Divide -3 to both sides:
Answer:
The side length is 2 ft
Step-by-step explanation:
A cube has a volume of
V = s^3
8 = s^3
Take the cube root of each side
8 ^ 1/3 = s^3 ^1/3
2 = s
You are correct in selecting choice A as the answer.
You need the middle angles between the two pairs of given congruent sides, so that you can prove the triangles to be congruent through SAS. The vertical angle theorem is used in this case. Alternate interior angles only come from parallel lines, but we dont know if any of the lines are parallel. Even if we did know the lines were paralle, we still wouldn't use the alternate interior angle theorem.
The answer is D because you would do factor by grouping