Zarena was reviewing the water bill for her dog day care and spa and determined that her highest bill, $3,800, occurred in May when she washed 400 dogs and her lowest bill, $2,400, occurred in November when she washed 200 dogs. What was the variable cost per dog associated with Zarenas water bill?

A) $6.00

B) $12.00

C) $9.50

D) $7.00

Phan Company sold 2,000 units in December at a price of $35 per unit. The variable cost is $20 per unit. The monthly fixed costs are $10,000. What is the operating income earned in December?

A) $30,000

B) $70,000

C) $20,000

D) $40,000