Mack's guitar fabrication shop produces low cost, highly durable guitars for beginners. Typically, out of the 100 guitars that begin production each month, only 80 percent are considered good enough to sell. The other 20 percent are scrapped due to quality problems that are identified after they have completed the production process. Each guitar sells for $250. Because some of the production process is automated, each guitar only requires 12 labor hours. Each employee works an average of 160 hours per month. Labor is paid at $11 per hour, materials cost is $42 per guitar, and overhead is $4,000. a. The labor productivity ratio for Mack's guitar fabrication shop is per hour. The multifactor productivity ratio for Mack's guitar fabrication shop is .