Two ferries start at the same time from opposite sides of a river.Each travels at a constant speed,but one is faster tha

Two ferries start at the same time from opposite sides of a river.Each travels at a constant speed,but one is faster than the other .They pass at a point 720m from the nearest shore.Both boat wait ten minutes before going back.On the return trip they meet 400m from the other shore .
How wide is the river