Kim Airedale, a manager of Waggers, Inc., was reviewing the water bills of a dog daycare and spa. She determined that its highest and lowest bills of $3600 and $2800 were incurred in the months of May and November, respectively. If 500 dogs were washed in May and 200 dogs were washed in November, what was the variable cost per dog associated with the company's water bill? (Round your answer to the nearest cent.)

A. $4.00

B. $14.00

C $7.20

D. $2.67