Given a right triangle, start thinking "Pythagorean Theorem" immediately. You know that the leg lengths are 10 cm and 24 cm; according to the P. Theorem, the length of the hypotenuse is:
h^2 = (10 cm)^2 + (24 cm)^2, or 676 cm^2. Taking the sqrt of both sides, we get:
h = length of hypotenuse = √676 = 26 cm