The angle is a right angle so therefore you can use Pythagorean theorem to find the value of hypotenuse x.
Theorem:
a^2+b^2=c^2, with C representing hypotenuse.
Substitute numbers:
7^2 + 3^2 = c^2
49+9=c^2
58=c^2
Square root to isolate c. Radical 58 is your answer.
