I've been stuck on how to do this question for over an hour. I clearly don't understand how to do it, hopefully somebody can help explain this to me?

Given:

$\displaystyle \sum\limits_{k = 1}^{100}{(6a_k + 8)} = 2000$

$\displaystyle \sum\limits_{j = 0}^{98}{(a_j_+_1)} = 545$

find a_{100}

Thank you.