A firm cleans chemical tank cars in the Bay St$.$ Louis area. With standard equipment, the firm typically cleaned $70$ chemical tank cars per month. They utilized $100$ gallons of solvent, and two employees worked $5$ days per week, $8$ hours a day. The company decided to switch to a larger cleaning machine. With the larger machine, they cleaned $60$ tank cars in only $4$ day per week. They utilized $130$ gallons of solvent, and the two employees worked $6$ hours a day. What is the change in labor productivity using labor$-$hour?