$p=0.7 x+6$ and the demand function is $p=\frac{193.6}{x+18}$. Answer:

Step 1 ：Set the two equations equal to each other: \(0.7x + 6 = \frac{193.6}{x + 18}\)

Step 2 ：Solve the equation for x, which gives two solutions: x = -30.57 and x = 4

Step 3 ：However, in the context of the problem, x cannot be negative because it represents a quantity (such as the number of units sold)

Step 4 ：Therefore, the only valid solution is x = 4

Step 5 ：Final Answer: The solution to the system of equations is \(\boxed{4}\)