Help with 2D waves

[wikidrox]

Here is the question

In a ripple tank experiment to demonstrate wave interference, two point sources having a common frequency of 6.0 Hz are used. The sources are 5.0 cm apart and vibrate in phase. A meter stick is placed in the water parallel to the line joining the sources. The central axis of the pattern crosses the meter stick at 50 cm. The first two nodal lines cross the meter stick at the 40 cm and 60 cm mark. Each of these points is 50 cm from the midpoint of the line joining the sources.

Find the wavelength.

I won't have a problem finding the wavelength if I could just understand how to set up the diagram. Please help.

[Doc Al]

I won't have a problem finding the wavelength if I could just understand how to set up the diagram.
Imagine an x-y plane. Let's put the two sources on the x-axis at x = -2.5 cm and x = +2.5 cm. The central axis of the pattern is along the y-axis. So the meterstick is placed parallel the x-axis (the 50 cm mark of the stick is at x = 0) at some value of y. You can figure out exactly where the stick is since you are told that the 40 cm and 60 cm marks are 50 cm from the origin.

Got it? Now draw it.