Explanation:

Let’s break it down:

- Shatabadi Express: 180 meters long, crosses a tree in 12 seconds.

Speed = 180/12 = 15 m/s.

- August Express: 240 meters long, also takes 12 seconds to cross a tree.

Speed = 240/12 = 20 m/s.

- Bridge is 270 meters long.

Now, to completely cross the bridge, each train must cover its length + bridge length.

- Shatabadi has to go 180 + 270 = 450 meters.

- August has to go 240 + 270 = 510 meters.

Time to cross the bridge:

- Shatabadi: 450 / 15 = 30 seconds.

- August: 510 / 20 = 25.5 seconds.

So, August finishes first.

Now, when August Express fully crosses (at 25.5 seconds), how much ground does Shatabadi have left?

- Shatabadi in 25.5 seconds: 25.5 × 15 = 382.5 meters.

- Left to go: 450 – 382.5 = 67.5 meters.

So:

Option 3—August, 67.5 m—is correct.