How many machines should be assigned to an operator for lowest$-$cost operations when

a$.$ Loading and unloading time on one machine is $1\mathrm{.}41$min.

b$.$ Walking time to the next facility is $0\mathrm{.}08$min.

c$.$ Machine time $($power feed$)$ is $4\mathrm{.}34$min.

d$.$ Operator rate is $$13\mathrm{.}20h.$

e$.$ Machine rate is $$\frac{18\mathrm{.}00}{h}.$