3/4" 4X8 plywood = 65 lb.
3x5 + 4x8 does not have a solution because it is not an equation. Are you looking for it's derivative? That would be: 15x4 + 32x7 Did you want it's indefinite integral? ∫(3x5 + 4x8) dx = x6/2 + 4x9/9 + C Or did you actually mean "three times five plus four times eight"? If so, the answer is 47.
$4.44 for a sheet of 4x8 1/2 in drywall at menards in Morris Illinois
If you mean 4x8 x 3/8 -then its about 38 pounds.