A retail store had sales of $42,100 in April and $55,750 in May. The store employs eight full-time workers who work a 40-hour week. In April, the store also had six part-time workers at 12 hours per week, and in May the store had eight part-timers at 15 hours per week (assume four weeks in each month). Using sales dollars as the measure of output, what is the percentage change in productivity (output in dollars per labor hour) from April to May? Note: Round your intermediate calculations and final answer to 2 decimal places