interference problem

[kidia]

Anyone can help me on this one.

 

A plane wave of wavelength [math]\lambda[/math]= 550 nm is incident normally on an opaque screen with three narrow parallel slits separated by distance [math]a[/math]= 2.3 mm. An interference pattern is observed on the other side of the screen at a large distance from it.

(a)At what angles are the first principal maxima adjacent to the central maximum?

(b)How does intensity, Imax, at the principal maxima compare to that from a single slit, I1?

 

in (a) can I use asin[math]\theta[/math]=m[math]\lambda[/math] to get the angle?