The correct answer to this question is this one: "D. 7, 13, 19, 25, 31, 37."
You can find a1+1 because you know the value of a1.
Now when you get to know the value of a1+1, you can get the value of a1+1+1. Repeat the cycle.
Because a2=a1+6, a2=7+6.
From that sequence, we can say that
a1 = 7
a2 = 13
a3 = 19
a4 = 25
a5 = 31
a6 = 37
