(c) (i) . (ii) is the slope of the line from the origin to the point .
(d) (i) has maximum slope at about (ii) If is maximum, then . (iii) at about 5.5 weeks. (iv) Since , the condition is . (v) When the current sales level equals the running average , then is maximum. Beyond that, is decreasing, which means that will also be decreasing.