1. A rectangular prism doesn't have the slant height. A rectangular prism has the height. A pyramid has the slant height. A cone has the slant height. 2.is not relevant to this problem. 3. If your prism is rectangular and NOT a square base, then the info "rectangular prism has a base of 8ft" is NOT ENOUGH for the solution. 4. DIAGNOSIS: there is no sense / (and it is not possible even to try) to solve so dirty formulated problem.