Solving Diffraction Grating Homework Problem

[ZxcvbnM2000]

Homework Statement

When a monochromatic light of wavelength 600 nm is viewed 2 m away through a diffraction grating, two similar lamps are observed, one on each side of it, and each 0.30 m away from it. Calculate the number of lines in the grating

Homework Equations

sinθ = (n*λ)/d

The Attempt at a Solution

I don't even know how to sketch the diagram !

From what i understand d=0.3 m but we don't know n !

 

[truesearch]

If the image is formed 2m away at a distance of 0.3m from the 'straight through' position I would take Sinθ to be approx 0.3/2
Use this in the equation with n=1 (1st order) to find 'd'
This gives you the separation of lines in the grating. To calculate the number of lines in the grating you need to know how wide it is and... this is not given.
Vague question