Klassen toy company, inc., assembles two parts (parts 1 and 2): part 1 is first processed at workstation a for 10 minutes per unit and then processed at workstation b for 20 minutes per unit. part 2 is simultaneously processed at workstation c for 30 minutes per unit. work stations b and c feed the parts to an assembler at workstation d, where the two parts are assembled. the time at workstation d is 15 minutes. a) the bottleneck of this process is workstation d , at 4 minutes per unit (enter your response as a whole number).