A chocolate bar manufacturer has been monitoring and trying to improve its productivity. The plant runs one 10-hour shift per day in a 5-day workweek. 15 employees work in the plant. In Week 1, 1250 units were produced. Management made some changes in the next two weeks, including hiring 2 more employees. In Week 4, 1,579 units were produced. What percent improvement in labor productivity (units/hr) did the plant achieve from Week 1 to Week 4