Wavelength of "Whip" CB Antenna on Car

[endeavor]

"A "whip" CB antenna on a car is 3.0 m long. When the car is moving along a highway, a standing wave is observed in the antenna that has 1.5 loop segments in it. What is the wavelength of the fundamental frequency of the antenna?"

I'm guessing that 1.5 loops segments mean that n = 3 in
$$L = n \frac{\lambda_{n}}{2}$$
$$L = 1.5\lambda_{3}$$
The fundamental frequency occurs when n = 1. So, since L = 3.0m,
$$\lambda_{1} = 6.0m$$

I know I must be doing something wrong, because the answer is 12m.

 

[endeavor]

If you are missing the LaTeX graphics, like I am, here's the equivalent:
let L = length, x = wavelength
L = n x_n/2
L = 1.5 x₃
x₁ = 6.0m