Ajax Carpet Cleaning Promises to Clean 100 Square Feet of Carpet

Ajax Carpet Cleaning promises to clean 100 square feet of carpet for $20.00. Their work standard for such a job is $5.00 for labor and $2.50 for cleaning supplies. Since they use the customer's electricity, there are no other inputs in to the cleaning process. What is their labor productivity?

A) 20.0
B) 4.00
C) 8.00
D) 2.50
E) 40.0