A computer factory produces 8400 computers per month at a constant rate, how many computers are built every 30 minutes assuming that there are 28 days in one month?  Choose the correct choice
A) 2.25 .
B) 3.125 .
C) 4.5 .
D) 5.225 .
E) 6.25 .

Rationale: "number of hours in 28 days = 28 * 24 number of 30 mins in 28 days = 28 * 24 * 2 number of computers built every 30 mins = 8400 / ( 28 * 24 * 2 ) = 6.25 answer e"
Answer: E