Hi there!
I'm going to assume that this is a right triangle that we are talking about here. To solve for the hypotenuse, we can use the pythagorean theorem.
WORK:
24^2 + 18^2 = c^2
576 + 324 = c^2
900 = c^2
c = 30 inches
Hope this helps!! :)
If there's anything else that I can help you with, please let me know!