How far apart are the ferryboats when they start their return trips?

[moe darklight]

post your answers in white . no pen or paper allowed.

Two ferryboats start at the same instant from opposite sides of a river, traveling across the water on routes at right angles to the shores. Each travels at a constant speed, but one is faster than the other. They pass at a point 720 yards from the nearest shore. both boats remain in their slips for 20 minutes before starting back. On the return trips they meet 400 yards from the other shore.

How wide is the river?I didn't get the right answer and then I felt like an idiot because the answer is really easy .

 

[Caracrist]

The answer is:
1760
yards

 

[Rogerio]

How wide is the river?

Well,
at the two moments the ferryboats meet, the relation between the distances covered by them is the same:
(w - a) / a = (2w - b) / (w + b)
So,
w = 3a - b = 3*720 - 400
w = 1760 yards

 

[moe darklight]

oops, totally forgot about this thread— yep, both right .