Surface area
2 triangles: Just do bh instead of 1/2bh, bh = 8 * 3 = 24
2 rectangles: 2bh but we first need to find h. The altitude pictured by dotted line, creates a right triangle where its hypotenuse is h. Since it also has side lengths 3 and 4, h = 5 (by pythag triplets). Then, 2bh = 2 * 12 * 5 = 120
base: bh = 12 * 8 = 96
Adding these areas we have 24 + 120 + 96 = 240
Volume: Bh (big b signifies area of the base)
B = area of the triangle = 1/2bh = 1/2 * 8 * 3 = 12
So Bh = 12 *12 = 144
Hope this helps you understand the process.