Answer:
C. 16
Explanation:
In order to find one side of a right triangle, given two sides, you can use the Pythagorean theorem:

We already have the values of one of the bases (12) and the hypotenuse (20), so we are looking for the second base. So, we have the values of B and C, and we need to find A.
To find A, put the values you already have into the formula as follows:

Next, square each value:

Subtract 144 from 400 to simplify the equation.

And finally, find the square root of 256 to find A.

Final answer:
C. 16
Have a nice day!