A person on a lighthouse 50 meters tall observes a boat moving directly away from it. Over a period of 10 seconds, the angle of depression to the boat changes from 60° to 30°. What is the approximate speed of the boat?

Two persons are on diametrically opposite sides of a tower. They measure the angles of elevation of the top of the tower as 30° and 60° respectively. If the height of the tower is 100 m, what is the approximate distance between the two persons?

At a point on level ground, the tangent of the angle of elevation of the top of a tower is found to be 56. On walking 70 m towards the tower, the tangent of the angle of elevation of the top of the tower is found to be 98. What is the height of the tower?