What is the Optimal Sound Frequency for Echoes Using a Single Slit?

[athymy]

Homework Statement

Hey guys, I'm having a hard time understanding this whole waves chapter and my teacher just gave us a tricky problem...

So you have a single slit and it accommodates 3-6 wave lengths across its diameter. Assume that the sound created when echoing off objects may be between 20Hz to 20,000Hz. The question is to find an effective sound frequency to use as an echo. (we are using that c = 340 m/s)

I have no idea how the single slit is related to this problem, I thought that it was used to calculate the distance to the dark fringes. And what is meant by "accommodates 3-6 wave lengths"?

Homework Equations

The only frequency formula I know is c = fλ
We know that c = 340m/s

The Attempt at a Solution

Well I don't know the frequency nor the wavelength so I really have no clue what I'm supposed to do next. So if anyone could give me some tips or point me in the right direction I would really appreciate it.

 

[athymy]

Does anyone have a clue on how to solve this problem because I'm totally lost...