Use Johnson's rule to determine the opfimal sequencing for the five jobs to be processed on two machines in a fixed order $($Machine $1$ before Machine $2).$The processing times in hours are given in the toble below.a$.$ What is the optimal sequence?b$.$ What is the total flow time for this sequence?c$.$ Which job is the first to be scheduled? Is it scheduled to be the first job or the last? Explain.