Please help explanation need it

56 + 77 + 88 + 99 = 320km²

Step-by-step 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

14.3

step-by-step explanation:

add all the numbers together.

9 + 12 + 15 + 16 + 17 + 17 = 86

now, divide 86 by how many numbers we have: 6.

86 / 6 = 14.3

a_n = a_1 + (n - 1)d

the first term is 6.

the common difference d = ?

when you find d, replace n with 7 and d with the common difference to find your answer.