How Many Days a Factory Needs to Make 5,000 Polo Shirts?

To find the answer to the above questions you must have the following
information

To make 5000 polo shirts-

Capacity required = 5000 X 16 minute = 80,000 minutes = 1333
Hours

Available Capacity/Day = 20 X 8 hours = 160 Hours

Assume that line works at 100% efficiency.

So, the Days required (theoretical) to produce 5000 polo shirts
= 1333 / 160 = 8.3 days (9 days)

If factory run at 50% efficiency then = 9 X100%/50% = 18
days

For planning add one more day as in practical one day will
be lost for loading and line setting.

If your production is calculated at 50% efficiency then you need 19 days to complete the above order.

For further accuracy, you can use Learning Curve to calculate day-by-day production increment up to pick production.