C - -7
To find this, use the arithmetic sequence:
an = a1 + (n - 1) to the power of d
a1 being the first number within the sequence, n being the place you are attempting to find, and d being the common distance between the already presented numbers.
With this information, you can set up the equation as so:
an = 6 + (14 -1) to the power of -1
Thus, giving you the answer of -7.
Hope this helps!
