Hi there!
Since we have a right-angled triangle, we can use the Pythagorean Theorem to find our answer. The Pythagorean Theorem states the following:
[tex] { a}^{2} + {b}^{2} = {c}^{2} [/tex]
In this formula a and b represent the legs of the triangle and c represents the length of the hypotenuse.
Let's substitute our data from the question.
[tex] {42}^{2} + 20 {}^{2} = c {}^{2} [/tex]
Square.
[tex]1764 + 400 = c {}^{2} [/tex]
Add.
[tex]2164 = c {}^{2} [/tex]
And finally take the root of both sides. We only need to use the positive solution, since the length of the hypotenuse can't be negative.
[tex]c = \sqrt{2164} [/tex]
The answer is B.
