Replace the letter

In the following question a series is given and it is followed by the starting point of another series. After this, a question is given, you have to complete the second series by applying the same logic as in the first given series, and then you have to answer the question.

    5     8     12     17     23     30
    9     a     b     c         d     e  

Which number should come in place of c?

Watch this space for answer in a week.