Two trains started at $7 \mathrm{AM}$ from the same point. The first train travelled north at a speed of $80 \mathrm{~km} / \mathrm{h}$ and the second train travelled south at a speed of $100 \mathrm{~km} / \mathrm{h}$. The time at which they were $540 \mathrm{~km}$ apart is _____________AM.
(A) 9
(B) 10
(C) 11
(D) 11.30
Two trains started at $7 \mathrm{AM}$ from the same point. The first train travelled north at a speed of $80 \mathrm{~km} / \mathrm{h}$ and the second train travelled south at a speed of $100 \mathrm{~km} / \mathrm{h}$. The time at which they were $540 \mathrm{~km}$ apart is _____________AM.
(A) 9
(B) 10
(C) 11
(D) 11.30