A boat is travelling away from the enemy watch tower and is at a distance of 200m from it. By the time enemy is ready to fire the gun,boat has traveled another 400m. The angle of depression of the boat w.r.t. to tower has doubled when compared to previous position. What should be the range of enemy's guns in order to hit the boat at its current location??

1) 400 rt 3
2) 500 rt 2
3) 600 rt 2
4) 500 rt 6