A stick 4 ft long, marked off in feet, is placed vertically at the shallow end of a swimming pool, where the water is 3 ft deep. The $1-\mathrm{ft}$ mark is at the surface of the water, the 4 -ft mark at the bottom. An observer stands at the opposite end of the pool with his eyes 20 ft horizontally from the stick and 7 ft above the water surface. What is the apparent depth of the 2 -, 3 -, and 4 - ft marks below the surface, as the observer would judge by comparison with the distance from the top of the stick to the 1-ft mark?