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Mathematics>Standard Multiple Choice
Read the following SAT test question and then click on a button to select your answer.
A machine can insert letters in envelopes at the rate of 120 per minute. Another machine can stamp the envelopes at the rate of 3 per second. How many such stamping machines are needed to keep up with 18 inserting machines of this kind?
(A)12
(B)16
(C)20
(D)22
(E)24
