Please need answer with all calculations please thank you….

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 for20minutes per unit. Part 2 is simultaneously processed at workstation C for15minutes 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 is12minutes.

​a) The bottleneck of this process is

workstation A

workstation C

workstation D

workstation B​,

at minutes per unit ​(enter your response as a whole​ number).