I think d would be the answer.
Errrrr, it has 80.
80 is the correct answer
So first we find the gap between the slits by the formula d=1/N
<span>N is number of lines per metre so 3700 line/cm = 370000 lines/m </span>
<span>So d=2.7*10^-6 </span>
<span>Now we use the formula dsin(angle)=n(wavelength) </span>
<span>d is the same </span>
<span>n is the order of the diffraction pattern </span>
<span>so wavelenth=dsin(angle)/n </span>
<span>=[(2.7*10^-6)*sin30]/3 </span>
<span>=4.5*10^-7 m</span>
