The enemy ship fled at a speed of 400 meters per minute at a distance of 7,000 meters from our island. Our navy fast ship immediately set off from the island. After 13 minutes, our fast ship fired at a distance of 500 meters from the enemy ship and sank the enemy ship. How much is our fast ship per branch? rice.
敌舰离我海岛7000米处以每分钟400米的速度逃跑，我海军快舰立即从海岛出发，13分钟后我快舰在离敌舰500米处开炮击沉敌舰，我快舰每分行多少米．
<result>3_900</result>