Six computers, each working at the same constant rate, together can process a certain amount of data in 6 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?	Choose the correct choice from the following answers
A) 3
B) 5
C) 6
D) 9
E) 12
Explanation: If six computers require 6 days to process the data, thats   a total of 36 computer-days the product of 6 and 6. If you change the number   of computers or the number of days, 36 will have to remain the product, whether   that means 36 days of one computer or one day with 36 computers.   In 4 days, the number of computers is:   4c = 36   c = 9   9 computers is 3 more than the 6 that it took to do the job in 6 days, so   the correct choice is (3).
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Six computers, each working at the same constant rate, together can process a certain amount of data in 6 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?