At the high level of activity in November, 7,000 machine hours were run and power costs were $12,000. In April, a month of low activity, 2,000 machine hours were run and power costs amounted to $6,000. Using the high-low method, the estimated fixed cost element of power costs is:
a. $12,000.
b. $6,000.
c. $3,600.
d. $8,400.