7. The bottom of a river makes a V-shape that can be modeled with the absolute value function, d(h) = 1/6 |h – 300| - 50 where d is the depth of the river bottom (in feet) and h is the horizontal distance to the left-hand shore (in feet). A ship risks running aground if the bottom of its keel (its lowest point under the water) reaches down to the river bottom. Suppose you are the harbor master and you want to place buoys where the river bottom is 20 feet below the surface. If one buoy is to be placed 120 feet away from the left shore, how far should the second buoy be placed form the left shore?
(Note: A buoy is an anchored float serving as navigation mark, to show reefs or other hazards to guide ships.)