Answer
n = 4
Work Step by Step
Since there are 3.55g of F for every gram of S when there is 6 moles of F for every mole of S, you can set up a proportion using the given fact that when there are n moles of F for every mole of S, there are 2.37g of F for every gram of S.
$\frac{6 mol}{3.55g}$=$\frac{n mol}{2.37g}$
n mol $\approx$ 4