Apparently k=6. It doesn't say it in the question, but I'll assume that you had a mistype and forgot to say that the second term is 12.
Anyway,
The nth term of a geometric sequence is
. Thus, the 52nd term would be 
and the 50th term would be 
When you divide the two, the 2's would cancel out and k^49 would cancel out, leaving you with 1 on the bottom and k^2 on the top. As we said at the beginning, k=6, so our answer is just 6*6=36.
Anyway,
The nth term of a geometric sequence is