Being that u have a set of data that has an even number of numbers, the median (middle number) would be found by adding the 2 middle numbers and dividing by 2.
ur 2 middle numbers would be 25 and x...and when added, u divide by 2, u will get 32.5...so lets set it up as an equation.
(25 + x) / 2 = 32.5...multiply both sides by 2 25 + x = 32.5 * 2 25 + x = 65 x = 65 - 25 x = 40 <== ur missing number