Answer:
56 + 77 + 88 + 99 = 320km²
Explanation:
A triangular prism has 5 sides. We can start with the top and bottom, which have a base of 7 km and a height of 8km, making each of their areas equal to 7 * 8/2 = 28. Adding those up, we get 28+28 = 56 km² as the surface area of the top and bottom portions.
Next, we have the face that has 7 as the base and 11 as the height. The area of that is 7 * 11 = 77km²
After that, we have the face with 8 as the base and 11 as the height, making the area of that 8 * 11 = 88km²
Finally, we have the face with 9 as the base and 11 as the height, making that area 9 * 11 = 99km²
Adding these all up, the total surface area is
56 + 77 + 88 + 99 = 320km²