Here it says, what is the maximum number of turns for an alpha helix that contains 72 residues? Alright. So we have 72 residues within this question. Now remember, we have a conversion factor. Our conversion factor says that for every one turn, we have 3.6 residues involved.

We're going to use this to help us find our answer. We want to cancel out residues, so we put that on the bottom. So we have 3.6 residues here on the bottom, and that's for every one turn that's on top. Here, my residues will cancel out, and at the end, I'd have my number of turns. So my end amount will come out to be 20 turns.

So here, this would mean that our answer would have to be option d, 20 turns.