Consider the following sequential production process with four machines A$,$ B$,$ C$,$ and D $(4$ workers operate these machines respectively, one worker per machine$).$Machine AMachine DFramerFinisher$5$ minutes minutesMachine BMachine CHandlerStringer$3$ minutes$10$ minutes$2$All flow units need to move through all the above stages sequentially, with the designated task time indicated above. Assume the labor rate is $$15$ per hour per employee, and the process is operated on a continual basis, what is the average labor cost per unit of product produced? $$50$ $$20$