Figure 3-1 Sonor Systems undertakes its own machine maintenance. The depreciation on the equipment is $20,000 per year and operating cost is $2 per machine hour. Last year 275,000 machine hours were used to produce 100,000 units. See Figure 3-1. If 300,000 machine hours had been worked last year, what would be the total machine maintenance cost? a. $600,000 b. $220,000 c. $620,000 d. $420,000