Hula Juice, a Smoothie Restaurant, Uses a Substantial Amount of Water

Hula Juice, a smoothie restaurant, uses a substantial amount of water in its operations. In August, the busiest month, the restaurant used 20,000 gallons of water at a cost of $600. In January, the slowest month of the year, 4,000 gallons of water were used at a cost of $200. The mixed cost formula for Hula's water usage is

A) $0.02 per gallon + $120.
B) $0.025 per gallon + $100.
C) $0.025 per gallon + $80.
D) $0.033 per gallon + $68.
E) none of the above.