Ajax uses the high-low method of estimating costs. Ajax had total costs of $50,000 at its lowest level of activity, when 5,000 units were sold. When, at its highest level of activity, sales equaled 12,000 units, total costs were $78,000. Ajax would estimate fixed costs as Select one:

a. $28,000 b. $30,000 c. $64,000 d. $128,000