It's obviously none of the above because the true area will have a square root of 3 in it because of the equilateral triangle. They want us to find the approximate area. When I was in school the difference between an approximation and the exact answer was greatly stressed but that seems to be fading of late.
That's a rectangle less an equilateral triangle. The area of an equilateral triangle is
which is easily derived but I won't bother here.
Answer: b