In the triangle below, what is the approximate value of x?

First, consider the Pythagorean rule:

small side ² + other side ² = hypotenuse²
           a²      +          b²       = c²

So in this case, to find the length of side b, follow the rule and calculate like so:

b²= c²- a²
b²= 24² - 12²
b²= 432
b  = √423
b  = 6√3 AKA 20.78

Therefore the correct answer is d).

Hope this helps!