Difficult Physics Question..Need Help!?

[Jess]

Having some difficulty solving these question any help would be appreciated.

Question 1
How many lines per centimeter does a grating have if the third-order bright fringe occurs at a 23.5° angle for 626 nm light?

Question 2
A parallel beam of light from a He-Ne laser with a wavelength 653 nm, falls on two very narrow slits 0.050 mm apart. How far apart are the fringes in the center of the pattern if the screen is 2.6 m away? Give your answer in cm.