Can Anyone Check My Work?

If a right triangle with legs of 8 and 16 inches had a hypotenuse of 17.5 inches, your work would be completely correct. However by the Pythagorean Theorem, a right triangle with legs of 8 and 16 inches has a hypotenuse of √(8^2 + 16^2) = 8√5 (approximately 17.8885) inches. Supposing that you want a right triangular prism with base this triangle and height 12 inches, your volume is correct but your area is too small by (8√5 − 17.5)*12 (approximately 4.6625) square inches.