Two trains A and B of length l and 4 l are travelling into a tunnel of length L in parallel tracks from…

Two trains $A$ and $B$ of length $l$ and $4l$ are travelling into a tunnel of length $L$ in parallel tracks from opposite directions with velocities $108 \mathrm{km} {\mathrm{h}}^{-1}$ and $72 \mathrm{km} {\mathrm{h}}^{-1},$ respectively. If train $A$ take $35 \mathrm{s}$ less time than train $B$ to cross the tunnel then, length $L$ of tunnel is:

(Given $L=60 l$)