i would recommend asking a tutor because some people answer just to get points
Check the picture below.
you really have two rectangles, a 6x10 and a 6x5, and surely you know what those areas are, so sum them up, and that's the area of the polygon.
So each dimention is 32 by 8 by 10
so the surface area=2 times(8 times 10)+(2 times (32 times 10))+(2 times (8 times 32))=2 times 80+2 times 320+2 times 256=1312
if halved
just divide each by 2
(2 times 4 times 5)+(2 times 16 times 5)+(2 times 4 times 16)=(2 times 20)+(2 times 80)+(2 times 64)=40+160+128=328
the new surface area is 328 mm^2
B is the correct answer.
8 x 35 = 280