You can look on the app Socratic to help you.
Letter A is right
Explanation: best of luck
To find the value of C: Use the Pythagorean Theorem
4^2 + 3^2 = c^2
16 + 9 = c^2
25 = c^2
sqrt of 25 = c
c = 5
10 x 10 x 10, I believe this is the form you mean.