A retail store has sales of $45,000 in April and $56,000 in May. The store employs eight full-time workers who work a 40 hour work week. In April the store also had seven part-time workers at 10 hours per week, and in May the store had nine part-timers at 15 hours per week. Using sales dollars as the measure output, what is the percentage change in the productivity from April to May?