At the end of an advertising campaign, weekly sales amounted to $\$ 19,000$ and then decreased by $8 \%$ each week after the end of the campaign.
a. Write the equation of the exponential function that models the weekly sales.
b. Find the sales 7 weeks after the end of the advertising campaign.
a. What is the equation for the retail price?
\[
\begin{array}{l}
y=19,000(9)^{x} \\
y=19,000(1.08)^{x} \\
y=19,000(0.92)^{x}
\end{array}
\]
b. Find the sales 7 weeks after the end of the advertising campaign.
(Do not round until the final answer. Then round to the nearest dollar as needed)

Step 1 ：Translate the problem into an exponential decay function. The general form of an exponential function is \(y = ab^x\), where \(a\) is the initial amount, \(b\) is the growth/decay factor, and \(x\) is the time. In this case, \(a = 19000\), \(b = 1 - 0.08 = 0.92\) (because the sales decrease by 8% each week), and \(x\) is the number of weeks after the end of the campaign.

Step 2 ：Substitute \(x = 7\) into the equation to find the sales 7 weeks after the end of the campaign.

Step 3 ：Calculate the sales 7 weeks after the end of the campaign using the equation \(y = 19000 imes (0.92)^7\).

Step 4 ：Final Answer: a. The equation of the exponential function that models the weekly sales is \(y = 19000 imes (0.92)^x\) b. The sales 7 weeks after the end of the advertising campaign is \(\boxed{10599}\) dollars.