Calculating Third-Order Maximum Angle for Grating

[rachiebaby17]

Homework Statement

A grating has exactly 7000 lines uniformly spaced over 2.67 cm and is illuminated by light from a mercury vapor discharge lamp. What is the expected angle for the third-order maximum of the green line ( = 546 nm)?

Homework Equations

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The Attempt at a Solution

no idea :(

 

[rl.bhat]

Try to find out the relevant equation for diffraction grating.