There are 8 workers at the Bessel Shirt Company. It takes each worker 12.5 minutes to make a shirt. How long would it take the eight workers

well it would take 8 workers  12.5/8 minutes to make one shirt - If it really worked that way.

so

it would take them 12.5/8*1200 minutes to make 1200 shirts

Assuming that all 8 workers start and stop at the same time,  8 shirts are produced in 12.5 minutes......then 1 shirt is produced every (12.5 / 8) = 1.5625 min

Then 1200 of them would take 1200 x 1.5625 minutes = 1875 minutes = 31.25 hrs...