Answer:
x = 18
Explanation:
This problem can be solved using concept of Pythagoras theorem.
Pythagoras theorem states that in a right angled triangle, if "a" and "b" are sides containing the right angle and h is hypotenuse then the relation between them is

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Given in the problem
a = 24
b = x
h = x+12
applying Pythagoras theorem

for (x+12)^2 we have used formula

Thus, value of x is 18.