$2.$ Presently, one operator is tending five identical machines. Each machine is used to produce similar products. With $5$ machines it has been observed that during a cycle a total of $20$ machine$-$minutes is consumed in machines waiting for service to begin. In the past, it was observed that the operator was idle for $10$ minutes each cycle when assigned to tend $3$ machines. If machining time is $25$ minutes and independent operator time is $1$ minute per machine cycle, what is the value for concurrent activity? If C$1$ equals $$4/$ hour and C$2$ equals $$6/$hour$,$ what is the economic assignment? What is the value of the minimum cost per unit produced?