representing the rate at which letters are processed then.
(i) Letters began to pile up when they arrived at a rate greater than that at
which they were being processed, that is, at t = 10 A.M.
(ii) The pile was largest when the letters stopped piling up, at t = 2 P.M.
(iii) The number of letters in the pile is represented by the area of the
small trapezoid above the horizontal line: .
(iv) The pile began to diminish after 2 P.M., when letters were processed
at a rate faster than they arrived, and vanished when the area of the
shaded triangle represented 1500 letters. At 5 P.M. this area is
letters, so the pile vanished shortly after 5 P.M.
Draw a vertical element of area as shown below.
(a) Let a represent the x-value of the positive point of intersection of y =
