Question 614442
1 clerk can process 75 pieces of mail in 2 and 1/2 hours
Note that 2 and 1/2 hours equals 150 minutes ({{{ 2.5*60 = 150 }}})
1 clerk can process 1 piece of mail in {{{ 150/75 = 2 }}} minutes
1 clerk can process 1620 pieces of mail in {{{ 2*1620 = 3240 }}} minutes
8 clerks can process 1620 pieces of mail in {{{ 3240/8 = 405 }}} minutes
Notes that {{{ 405/60 = 6.75 }}}, so the answer is 6 hours and 45 minutes