Question 183471
By definition, a "right triangle" means one of the interior angles has a measurement of 90 degrees.  As such, you can apply the Pythagorean theorem:
a^2 + b^2 = c^2
where
c is the hypotenuse (the length of the side opposite the 90 deg)
'a' and 'b' are the lengths of the other two sides
.
First, before you begin, all units must be the same.  So, let's convert the length 36 inches to feet.  There are 12 inches per feet so 36 inches is the same as 3 feet (3x12).
.
Let x = the length of the missing side
then
x^2 + 3^2 = 5^2
x^2 + 9 = 25
x^2 = 16
x = 4 feet