From the top of a cliff 200 m high, the angles of depression of the top and bottom of a tower are found to be 30° and 60° respectively. If the tower and the cliff are on the same side of a river, what is the width of the river?

A tower stands vertically on the ground. From a point on the ground which is 20 m away from the foot of the tower, the angle of elevation of the top of the tower is found to be 60°. What should be the height of another tower on the opposite side of the same point, if the angles of elevation of the tops of the two towers from that point are complementary?

A man on the top of a vertical observation tower observes a car moving at uniform speed towards the tower. If it takes 12 minutes for the angle of depression to change from 30° to 45°, how much more time will it take for the car to reach the tower?

A person standing on the bank of a river observes that the angle subtended by a tree on the opposite bank is 60°. When he retreats 40 m from the bank, he finds the angle to be 30°. What is the breadth of the river and the height of the tree?