can someone help :)) and pls explain how u got it so i can understand

Answer:
B) x = 20
Step-by-step explanation:
The formula for finding the missing side of a right triangle is: a^2+b^2=c^2.
C represents the longest side of the right triangle, so if we plug in the given lengths, we can solve: 12^2 + 16^2 = x^2
Solve the exponents: 144 + 256 = x^2
Add: 400 = x^2
Find the square root: 20 = x