I think the answer is 17
Explanation: To find a missing side of a right triangle you need to do the Pythagorean theorem which is a^2xb^2=c^2. The side lengths are 15 and 8. If you substitute that I. Then it’s 15^2x8^2=c^2. 15^2 is 225 and 8^2 is 64. So the equation is now 225+64=c^2. 225+64=289. 289=c^2. Now all we have to find is the square root of 289 which is 17. So c , or in the case of your problem x is equal to 17.