Problem
A firm cleans chemical tank cars in the Edmonton area. With standard equipment, the firm typically cleaned 70 chemical tank cars per month. They utilized 10 gallons of solvent, and two employees worked 20 days per month, 8 hours a day. The company decided to switch to a larger cleaning machine. Last December, they cleaned 55 tank cars in only 15 days. They utilized 12 gallons of solvent, and the two employees worked 6 hours a day. What is the percentage (%) change in labor productivity?