Be sure to know and understand the following:
If there is a common difference between terms of a sequence, the sequence is arithmetic. Example: 108 110 112 114 (common diff is 2). But with 108, 66, 141, 99, the diff between 108 and 66 is -42; the diff between 66 and 141 is 77; and so on. -42 and 77 are not the same. So, what do you conclude?
If there is a common ratio, the sequence is geometric. Example: 108, 216, 324, 648. What do you conclude about the given sequence?