CAT 2018 Progression — Previous Year Question

Let $t_1, t_2, \ldots$ be real numbers such that $t_1 + t_2 + \cdots + t_n = 2n^2 + 9n + 13$, for every positive integer $n \geq 2$. If $t_k = 103$, then $k$ equals [TITA]