We can begin by taking each part of the table and writing it out as a term of the geometric sequence. For example, for n=4, we have ar^3=6, and for n=9 we have ar^8=-192. Then, we can divide these two terms to get r^5=-32. Taking the fifth root on both sides, we get that r=-2. We can then just plug this in, getting -8a=6, or that a=-3/4, giving us B.
