Diffraction Grating problem (AQA - A, June 2005, section A Q6)

Hi there folks, this is my first post but what better way to start than a question about diffraction gratings.
As I said in the thread title, the particular question thats bugging me is question 6 off the AQA A syllabus, June 2005.
The question reads:

''Light of wavelength λ is incident normally ona diffraction grating for which adjacent lines are a distance 3λ apart. What is the angle between the second order maximum and the straight through position?''

Its a multiple choice and the answers are:

a.) 9.6°
b.) 20°
c.) 42°
d.) There is no second order maximum

Now basically this has me confused, as normally for these questions I would use d SinΘ = nλ but I don't see how that would work?

Anyway, if any of you kind folk could explain the procedure for working this out, I'd be much obliged. Thanks, Andy x