The hypotenuse is 5, the sides are 3 and 4. The perimeter is the addition of those 3 numbers.
5+4+3 = 12 units
For future reference, if the sides of a right triangle are any multiples of 3 and 4, the hypotenuse is the same multiple of 5. This triangle has sides with lengths 3, 4, and 5, and a triangle with sides 9 and 12 would have a hypotenuse of 15 :)
