GRE Big Book Test 2 Section 2 Q5 page 76

This is a Quant comparison question:

Rectangular region R has width 8 and perimeter 40.

a. The Area of R b.256

my answer: (B)
reasoning: 8+8+x+x = 40
x = 12 ===> 12*8 < 256
Books answer: (C)

How is the answer C?

width != perimeter.

okay, how would you solve it?
your explanation isn’t exactly a solution

OK for some reason I misread the problem. Answer is indeed B, are you looking at the wrong answer key by chance?