The rate of sales (in sales per month) of a company is given, for t in months since January 1, by

r(t) = t⁴ − 20t³ + 118t² − 180t + 200.

(a) Graph the rate of sales per month during the first year (t = 0 to t = 12). Does it appear that more sales were made during the first half of the year, or during the second half?
(b) Estimate the total sales during the first 6 months of the year and during the last 6 months of the year.
(c) What are the total sales for the entire year?
(d) Find the average sales per month during the year.