Depreciation expense homework help?

Check your instruction again. Are you sure you should be taking the residual from the original cost? I think your equation isn't set right either. Can't help you much till I get home later where my accounting book and my calculator is, but I think before I get there you can find the answer you need. Check if you're right on deducting the residual from the original, then see if you are correct in using the (1/8) in the equation. I think that's probably 8/12 or something using a yearly denomination.