According to the question, it takes 6 minutes for a train to travel more than1000 m per minute, so it travels within 4 minutes100 * 6 = 600 m.

The original speed is 600/4= 150m/ min,

Then the distance of driving 10 minutes is150 *10 =1500m.

The length of the bridge is1500-400 =1100m.