Between each pair of terms in this sequence is the amount the sequence is decreasing by. The 𝒏th term refers to a term's position in the sequence, for example, the first term has 𝒏 = 1, the second ...

First find the common difference between each term and the next. In this case, every time you move along one position (n + 1), the term goes up by three (s + 3). This is three times as much and this ...