This is a simple alternating subtraction and addition series; The first series begins with 1 and adds 6; the second begins with 20 and subtracts 4, and so on.
Fill in the blank with the correct number in this number series: 1, 20, 7, 16, __, 12, 19, ?
Options:
[a] 14
[b] 12
[c] 13
[d] 15
[e] 11