It's J. Honestly I just picked a number for X and a number for C and solved it using each answer. J works.
2/7 is the answer i think
The next item in the sequence will be -18, as the sequence is subtracting 4, then subtracting 6, then subtracting 4, and so forth. To continue the sequence, the next number will be 4 less than -14, which is -18.
Hope this helps!!