This is an example of an arithmetic sequence. First, we need to find common difference. (a(4) = the 4th term of the sequence).
5 - 3 = 2
7 - 5 = 2
Since the common difference is 2, we can just add this to a(3) to find teh 4th term.
7 + 2 = 9
Therefore, a(4) = 9.
Best of Luck!
