Тhe longest side of the right triangle is the hypotenuse. The third angle of this triangle is 90 - 60 = 30° The short leg is the side opposite the 30 degree angle. In a 30-60-90 triangle the side opposite the 30 degree angle is half the length of the hypotenuse. If the the hypotenuse = 10 inches then the short leg = 10/2 = 5 inches