16 Jim has a triangular shelf system that attaches to his showerhead. The total height of the system is 18 inches, and there are three parallel shelves as shown above. What is the maximum height, in inches, of a shampoo bottle that can stand upright on the middle shelf?

Step 1 ：The question is asking for the maximum height of a shampoo bottle that can stand upright on the middle shelf. Since the total height of the system is 18 inches and there are three shelves, we can assume that the shelves are evenly spaced. Therefore, the maximum height of a shampoo bottle that can stand upright on the middle shelf would be the total height divided by the number of shelves.

Step 2 ：Let's denote the total height as \(total\_height\) and it is 18 inches.

Step 3 ：Let's denote the number of shelves as \(number\_of\_shelves\) and it is 3.

Step 4 ：We can calculate the maximum height of a shampoo bottle that can stand upright on the middle shelf as \(max\_height = \frac{total\_height}{number\_of\_shelves}\).

Step 5 ：Substitute the given values into the equation, we get \(max\_height = \frac{18}{3} = 6.0\).

Step 6 ：Final Answer: The maximum height, in inches, of a shampoo bottle that can stand upright on the middle shelf is \(\boxed{6}\).