Since the start of July, OHaganBooks.com has seen its weekly sales increase. OHaganBooks.com fits the curve w(t) = 3612 + 251+ + 6,244 (0 5 + 5 6) to its weekly sales figures as shown in the following graph. w (book sales) 9,000 8,500 8,000 7,500 7,000 6,500 + t (week) (a) Compute the derivative function w(t). W ( t ) = (b) According to the model, what was the rate of increase of sales at the beginning of the second week (t = 1)? books per week (c) If we extrapolate the model, what would be the rate of increase of weekly sales at the beginning of the eighth week (t - 7)? books per week