Six computers, each working at the same constant rate, together can process a certain amount of data in 12 days. How many additional computers, each working at the same constant rate, will be needed to process the same amount of data in 4 days? Select the correct option.
A) 3	B) 5	C) 6	D) 9	E) 12
Explanation: If six computers require 12 days to process the data, thats   a total of 72 computer-days the product of 6 and 12. If you change the number   of computers or the number of days, 90 will have to remain the product, whether   that means 72 days of one computer or one day with 72 computers.   In 4 days, the number of computers is:   4c = 72   c = 18   18 computers is 12 more than the 6 that it took to do the job in 12 days, so   the correct choice is (12).
<result>E</result>
Six computers, each working at the same constant rate, together can process a certain amount of data in 12 days. How many additional computers, each working at the same constant rate, will be needed to process the same amount of data in 4 days?