How many terms are in the arithmetic sequence 7, 0, −7, . . , −175?

So hmmm 7, 0, -7.... what the dickens is going on?   hmmm is really dropping each time by 7, so, 7-7, 0, and 0-7, -7 and so on.

so, the "common difference" is then -7, and our first term is 7, now, who's -175?  let's check.