In 2011, Modern Electronics, Inc. produced 60,000 calculators, employing 80 workers, each of whom worked 8 hours per day. In 2012, the same firm produced 76,500 calculators, employing 85 workers, each of whom worked 10 hours per day. Productivity at Modern Electronics

a. decresed by 4%
​b.remained constant
c.increased by 8.33%
d.increase by 27.50%