so a triangular prisim is like a triangle stacked on top of x number of identical triangles making a height, like a piece of paper made into a stack
so
basically find the area of each side and add
look at diagram/attachment
find area of triangle
1/2 b times h= area of 1 triangular face
multiply by 2 because 2 sides so 1/2 times 2 b times h=b times h
then 3 other sides
find area of each side and add
areas=(H times B)+(H times c)+(H times a)
so SA=(b times H)+(H times B)+(H times c)+(H times a)