21. Refer to Table 13-6. Each worker at the Wooden Chair Factory costs $12 per hour. The cost of each machine is $20 per day regardless of the number of chairs produced. Assume the number of machines does not change. If the factory produces at a rate of 78 chairs per hour, what is the total machine cost per day? a. $20 b. $40 c. $240 d. We are unable to determine total machine costs from the information given. 22. Refer to Table 13-6. Each worker at the Wooden Chair Factory costs $12 per hour. The cost of each machine is $20 per day regardless of the number of chairs produced. If the factory produces at a rate of 35 chairs per hour, what is the total labor cost per hour? a. $40 C. $384 b. 548 d. $424