Ahaha, T.T Sadly there is no easy way to find out the answers, but I will explain it to you as simply as possible ^^~
A² + B² = C²
C² = The longest side or Hypotenuse
After that, just substitute the given values:
When you get the answer, it would have been squared (n²) 'n' represents number you would have gotten~
So you just square root it, to find the original value~
Oh, and if you are given another value instead of C² use this formulae~
B² = C² - A²
A² = C² - B
The pictures are from Google and my school website, I hope it helps and Good luck!