7*8-4(6-2)+18
56-4(4)+18
56-16+18
40+18
58
6^2-(8*3)+2^2(7*3)
36-24+4(21)
12+84
96
Let me walk you through this real quick:
-4x + 9 (10x - 1)
-4x + 90x - 9 (open up the brackets)
90x - 4x - 9
= 86x - 9
Mean absolute deviation of the set is 1.6
Surface area is the sum of the areas of each side of a three dimensional object.
There are two sides that are 11x9, two sides that are 9x3, and two sides that are 11x3.
So the surface area is:
2(11)(8)+2(9)(3)+2(11)(3) = 296 ft^2