The set of series given are
13, 21, 29, 37
The number of terms is calculated as
Tn = a + (n - 1)d
The first term is 13
To find the common difference, we need to substract the lowest from the highest number
21 - 13 =8
29 - 21 = 8
37 - 29 = 8
The common difference is 8
The 16th term is
T 16 = 13 + (16 - 1) x 8
Solve the parentheses first
T16 = 13 + (15) x 8
T16 = 13 + 120
T16 = 133
The 16th term of the series is 133