A bread-making factory has the production process shown in the figure belov There are five operations in sequence. The product only needs to go through one of the parallel machines in each case where parallel machines exist. Wha is the bottleneck time per batch of this process? Proof Mix 60 min./batch Bake Pack 50 min/batch 60 min./batch 40 min./batch Proof Cut 60 min./batch 35 min./batch Mix B Pack 50 min/batch Proof 60 min./batch 40 min./batch 60 min./batch 35 min. 20 min. 50 min. 60 min. 30 min