A group of 5 Clarks have been assigned to insert 24000 letters into envelopes. The clerks perform this work at the following rates of speed Clerk A, 1100 letters an hour;Clerk B, 1450 letters an hour;Clerk C, 1200 letter an hour, Clerk D, 1300 letters an hour; Clerk E, 1250 letters an hour. At the end of 2 hours of work, Clerks C and D are assigned to another task. From the time that Clerks C and D were taken of the assignment, the number of hours required for the remaining clerks to complete this assignment is: