Remember that the area of a rectangle is length times width; since we don't know the width, we'll use the Pythagorean theorem to find it first:
Where l is the leg, and h the hypotenuse. We know that one of the legs, the base has a measures 34.3 inches and the hypotenuse a measures 42.1 inches.
Replace the values to get:
Now that we know the width (w), we just net to multiply it by the length to get our area:
We can conclude that the correct answer is
B) 836.9 in.