Larry's Auto Body Repair Shop had revenues that averaged $60,000 per week in April and $50,000 per week in May. During both months, the shop employed six full-time (40 hours/week) workers. In April the firm also had four part-time workers working 25 hours per week but in May there were only 2 part-time workers and they only worked 10 hours per week. What is the percentage change in labor productivity from April to May for Larry's Auto Body Repair? (Assume four weeks in each month and equal productivity for each hour worked.)