The following information is available for a company's utility cost for operating its machines over the last four months.

Month Machine hours Utility cost
January 1,050 $6,600
February 1,950 $7,200
March 2,700 $8,100
April 750 $4,530

Using the high-low method, the estimated variable cost per unit for utilities is:

a. $1.500
b. $3.600
c. $6.000
d. $3,300
e. $2,100