Because this is a triangle and we know that we can use the Pythagorean Theorem to find the hypotenuse we just plug in the numbers. But because you have the hypotenuse already you will subtract the leg from the hypotenuse.
A^2+B^2=C^ 16^2+B^2=20^2 256+B^2=400 subtract 256 from both sides B^2=144 now take the square root of both sides B=12
The second leg is 12 cm long. Your answer is B, the second answer.
