Choose the congruence theorem that you would use to prove the triangles congruent

It would be the HL theorum.

Step-by-step explanation:

The answer would be the HL theorum by just considering the name.  "HL" stands for Hypotenuse-leg.  The problem tells you that both triangles share the same length of their hypotenuse (The Hypotenuse is the line with one dash in it, or the one opposite of the 90 degree angle) and one of the legs (The legs are the lines that connect to make the 90 degree angle).  This makes the triangle congruent because if 2 sides of a triangle are the same it means that the third one is congruent as well.

the answer is 62.8 cubic units