If the leg of a right triangle are 3 ft and the 4ft the length of the hypotenuse is

Since the triangle is a right triangle, you can use the Pythagorean Theorem to find the length of the hypotenuse.
The Pythagorean Theorem: a² + b² = c², where c is the hypotenuse of the triangle.

Plug in the leg lengths and solve.

    a² + b² = c²
    3² + 4² = c²
    9 + 16 = c²
          25 = c²
            5 = c

The length of the hypotenuse is 5 ft.

The hypotenuse would be 5 because it is one of the Pythagoream Theorem triplets.