5. [5 pts] A machine shop uses ceramic cutter each costs $80 a piece which can be re- sharpened 4 times before disposal. In cutting certain high carbon steel materials, the cutting speed to ensure maximum material removal rate was found to be 58.9 ft/min while the resulting tool life was 34 min. To change cutting edge and to re-sharpen a tool typically takes 15 minutes. Estimate the best cutting speed (in ft/min) to minimize total cost. The rate of labor and other non-tool cost is $5/min for this machine shop.