Hitchcock, Inc., uses the high-low method to analyze cost behavior. The company observed that at 12,000 machine hours of activity, total maintenance costs averaged $7.00 per hour. When

activity jumped to 15,000 machine hours, which was still within the relevant range, the average cost per machine hour totaled $6.40. On the basis of this information, the variable cost per

machine hour was:

A. $4.00.

B. $6.40.

C. $6.70.

D. $7.00.

E. an amount other than those listed above.