Hi Dannielle,

You use Pythagoras theorem. The theorem says that if a right triangle has side lengths a, b and c where c is the length of the hypotenuse (the side opposite the right angle) then a² + b² = c².

For example suppose you have sides of length a = 3 inches and b = 4 inches then by Pythagoras theorem a² + b² = c² so 3² + 4² = c² and thus c² = 9 + 16 = 25 and hence c = √25 = 5 inches.

Now try your numbers,
Penny