Answer:
One triangular face = 7.5mm2
Surface area=135mm2
Explanation:
Area of a triangle (1/2)(bh) so (1/2)(2.5*6)=7.5
The area of the first rectangle is 20 (2.5*8)
The second rectangle is 52 (6.5*8)
The third rectangle is 48 (8*6)
Then you take the area of one triangle and multiply it by 2, which equals 15.
Then you add it all together and get 135