In the "front" we have a 6 - 8 - 10 right triangle
The area of this triangle = (1/2)(6 * 8) = 24
The base is a 10 - 24 - 26 right triangle
The area of this triangle = (1/2) ( 10 * 24) = 120
Another triangle is one with a base of 24 and a slant height of 6.....its area (1/2) (24 * 6) = 72
And the triangle at the "back" has a base of 26 and a height of 8
Its area = (1/2)(26)(8) = 104
So......the total surface area = (24 + 120 + 72 + 104) = 320 in^2
The volume= (1/3) area of base * height = (1/3) (120)( 8) = 320 in^3