If a diffraction grating has 3700 lines per cm, what is the spacing d between lines

So first we find the gap between the slits by the formula d=1/N

N is number of lines per metre so 3700 line/cm = 370000 lines/m

So d=2.7*10^-6

Now we use the formula dsin (angle) = n (wavelength)

d is the same

n is the order of the diffraction pattern

so wavelenth=dsin (angle) / n

=[ (2.7*10^-6) * sin30]/3

=4.5*10^-7 m