Trig problem I need help understanding.

Answer: 4√27
Step-by-step explanation: Using the Pythagorean theorem(a^2+b^2=c^2) you can see that 12^2+x^2=24^2. You can simplify that to get x^2+144=576 or, x^2=432. Therefore, x=√432 or in simpler terms, x=4√27