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

(Given $\mathrm{L}=60 l$ )