Use Pythagorean Theorem.
a^2 + b^2 = c^2
Substitute the numbers.
12^2 + b^2 = 20^2
144 + b^2 = 400
Subtract 144 from each side.
b^2 = 256
Take square root.
The answer is
b = 16
It’s the last one:
Area is length times width
So you first have to add the length
The once you get that new value, you multiply it times the width
B is the best answer for this problem.
Sorry if I’m wrong