Please give answer and explain how you got it because I'm so confused PLZ

It’s 15. You have to look at the triangle as a whole and use phytagoras theorem.

First step is to get rid of the square root. remember that a square root is the same as raising to the (1/2) power. see below: multiply exponents per exponent rules to get: remember you subtract exponents from the denominator and add exponents in the numerator so: simplify further: so a is the correct choice. if you don't understand this google exponent rules and it will you understand. look at the image results.

How many is in each case if there is 12 in each case it would be 40