Here, it helps to find a general expression for the nth term in the
sequence. Since the sequence is arithmetic, the general term is a_n = a +
bn, where b is the common difference. By inspection of the first few
terms we see the common difference is -4. Then by solving a_1 = a - 4x1 =
5, we obtain a = 9, so the nth term is: a_n = 9-4n. We then solve
a_n=-111 for n, so 9-4n=-111. Rearranging, we get 4n=9+111, or 4n=120,
or n=30. Thus there are 30 terms in the sequence.
