In the production process shown below, the drilling operation occurs separately from, and simultaneously with, the cutting and polishing operations. A product needs to go through only one of the three assembly operations $($the operations are in parallel$).$

Cutting process: $15$ minutes$/$unit

Polishing process: $10$ minutes$/$unit

Drilling process: $25$ minutes$/$unit

Pressing process: $40$ minutes$/$unit

Assembly process: $60$ minutes$/$unit $($divided into $3$ assembly stations $-$ each station is $20$ minutes$/$unit$)$

If this company operates $8$ hours per day, $20$ days per month, the monthly capacity of the manufacturing process is:

a$.960$ units$/$month

b$.384$ units$/$month

c$.160$ units$/$month

d$.240$ units$/$month