15) Gribble Company's high and low level of activity last year was 60,000 units of product produced (4pts) in May and 20,000 units produced in November. Machine maintenance costs were $156,000 in May and $60,000 in November. Using the high-low method, determine an estimate of total maintenance cost for a month in which production is expected to be 45,000 units. $120,000 $135,000 $117.000 E $144,000 None of the above