First term, a = 4
Fifth term = 16
The nth term of arithmetic sequence : a + (n - 1)*d
For fifth term, n = 5
a + (n - 1)*d
Substitute n = 5, a = 4, d = ?, 5th term = 16
4 + (5 - 1)d = 16
4 + 4d = 16
4d = 16 - 4
4d = 12 Divide by 4
d = 12/4
d = 3.
Recall the nth term is: a + (n - 1)*d = 4 + (n - 1)*3
4 + (n - 1)*3
4 + 3n - 3
3n + 4 - 3
3n + 1
So the nth term is 3n + 1. Option B.
Hope this helps
