To find the surface area you will need to find the area of all 5 surfaces (faces) on the prism. On a triangular prism there are 2 triangular faces and 3 rectangular faces. All 3 rectangular faces are the same and the 2 triangular faces are also the same.
To find the area of the triangular faces, you will use the formula for finding the area of a triangle:
A = 1/2bh
1/2 x 10 x 8.7
A = 43.5 in^2
To find the area of the rectangular faces, you will use the formula for finding the area of a rectangle:
A = bh
10 x 3
A = 30 in ^2
30 + 30 + 30 + 43.5 + 43.5 = 177
The minimum amount of wrapping paper needed for the gift is 177 square inches.
