After discontinuing all advertising for a tool kit in 2010, the manufacturer noted that sales began to drop according to the model
S = 500,000 / 1 + 0.1ekt
where S represents the number of units sold and t represents the year, with t = 0 corresponding to 2010 (see figure). In 2014, 300,000 units were sold.

(a) Use the graph to estimate sales in 2020.
(b) Complete the model by solving for k.
(c) Use the model to estimate sales in 2020. Compare your results with that of part (a).

500,000 - 450,000- 400,000 350,000 300,000 E 250,000 - 200,000 150,000 - 100,000 50,000 ++++ +++H 1 2 3 4 5 6 7 8 9 10 11 12 Year (0 + 2010) Number of units sold