4. Midland Motors manufacturers custom motors for high-end customized versions of cars and trucks. They have just started making a newly designed engine. Suppose Midland Motors used a 90% cumulative unit-time learning model. Direct material cost $9,000 per engine. Direct manufacturing labor time for first unit: 125 direct manufacturing labor hours. Learning curve for manufacturing labor time per engine: 90% cumulative average time. Direct manufacturing labor cost $43 per direct manufacturing labor-hour. Variance manufacturing overhead cost: $22 per direct manufacturing labor-hour. For a 90% learning curve, b= ln .9 / In 2 =-.1053605 7.693147 =-.152003 Calculate the total variable cost for producing 2 units $ 3 units $ 4 units $