1) if the 298 term of S is -616, and each thereafter is 2 less than the preceding term, you know that term 297, or 298 can also be solved, that's sufficient enough to find the 293rd term.
2) the stem is tricky because the question wants you to carry over and second guess yourself, or make you choose C, so be careful,
for statement 2: you still need a base to start, such as statement 1), 298 term of s is -616, and 2) you're lacking the difference per term, such as statement 1), the difference is -2 per term. So lacking these two makes this statement NOT SUFF.
Common Sense, really. NO MATH!
Kudos is this helps !