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

a$.$ Loading machine standard time$=0\mathrm{.}55$ minute

b$.$ Unloading machine standard time$=0\mathrm{.}35$ minute

c$.$ Walk$-$time between two machines$=0\mathrm{.}10$ minute

d$.$ Power$-$feed time $($machine time$)=1\mathrm{.}60$ minute

e$.$ Operator rate$=$$$18/$hr

f$.$ Machine rate$=$$$15/$hr

Draw an operator machine chart for the optimal solution. Show your calculations.