Does anyone know how to do this???

Answer:
You need to use Pythagorean's Theorem.
Step-by-step explanation:
In mathematics, the Pythagorean theorem, also known as Pythagoras' theorem, is a fundamental relation in Euclidean geometry among the three sides of a right triangle. It states that the square of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides.
a^2 + b^2 = c^2.