Sequence and Series: JEE Main 2026 Mathematics question

The common difference of the A.P.: $a_1,a_2,\ldots,a_m$ is 13 more than the common difference of the A.P.: $b_1,b_2,\ldots,b_n$. If $b_{31}=-277$, $b_{43}=-385$ and $a_{78}=327$, then $a_1$ is equal to