5a^2 - 6a -4 - (<span>-7a^2 + 3a -9)
=</span>5a^2 - 6a -4 + 7a^2 - 3a + 9
=12a^2 - 9a + 5
answer
12a^2 - 9a + 5
#11 and #12 have no solutions, #13 has a solution which is 14
Check the picture below.
so, to get the area of the triangles, we can simply run a perpendicular line from the top to the base, and end up with a right-triangle with a base of 22 and a hypotenuse of 34, let's find the altitude.

so then the surface area of the triangular prism is,
22.9 is the closest but not exact. It was probably rounded off.
I used the formula: leg^2+leg^2=hypotenuse^2
(You can use that formula for any right triangle.)