Five weeks ago, Star City began accepting electronic payments at the city's parking meters. The table shows the number of drivers who parked at one of the city's meters and paid cash to park during each week since it became an option to pay electronically. Week Cash Paying
Drivers
1 18,428
2 17,926
3 17,102
4 16,361
5 15,213

Assuming that the relationship is exponential, which is the best estimate of the number of drivers who will park their cars and pay by cash 9 weeks after it became an option to pay electronically?