Waves: velocity, frequency, wavelength

[bleucat]

Homework Statement

If you slosh the water back and forth in a bathtub at the correct frequency, the water rises first at one end and then at the other. Suppose you can make a standing wave in a 135 cm long tub with a frequency of 0.31 Hz. What is the velocity of the water wave?

Homework Equations

I know $$v = f \lambda$$ and that $$f = \frac{1}{T}$$, with $$v$$=velocity, $$f$$=frequency, $$\lambda$$=wavelength, and $$T$$=period.

The Attempt at a Solution

Okay, so this looked easy enough, right?
I converted 135 cm to 1.35 m and multiplied 1.35 x .31. This isn't the correct answer, however, and I am rather stymied. Am I missing something easy?

 

[Snazzy]

I believe that the frequency represents the fundamental frequency, ie. the bathtub length is half a wavelength.