When solving these types of problems just ignore the “shorter leg” or “longer leg” and focus on the lengths. Pythagorean’s Theorem is used in this problem. Since a leg and hypotenuse length are given then you you set the problem up as 9^2+b^2=15^2. You then do the squares so that it is shown as this, 81+b^2=225. Next you need to subtract 81 on both sides of the equation to isolate the variable b (or the missing leg length) which leaves you with b^2=144. Next to isolate the variable completely you do the square root of both b^2 and 144 which leaves you with the answer b=12. The leg is 12cm long.