Uh i do not get the pythagorean theorem.

A²+b²=c²
The hypotenuse of the triangle is c. (the slanted line, if it is a right triangle)
Simply fill in the variables, square them, and solve for the missing number.
Check out the picture, it is just an example.
Don't forget: the variable you are finding needs to be squared, that means that when you find your answer, find the square root of it.
↓↓↓↓

It is A

Step-by-step explanation: