APPROACH #1:
Before test day, it's useful to memorize the following Pythagorean triplets:
3-4-5
5-12-13
7-24-25

Although the first two triplets appear much more frequently on the GRE, the third one also shows up occasionally.
So if the two legs have lengths 7 and 24, the hypotenuse must have length 25, in which case the two quantities are equal.
Answer: C


APPROACH #2:
Since we have a right triangle, we can apply the Pythagorean theorem to write: 7² + 24² = hypotenuse²
Simplify: 49 + 576 = hypotenuse²
Simplify: 625 = hypotenuse²
Solve....hypotenuse = 25
Answer: C


Cheers,
Brent