<PRE><B>Question 31062</B>
Let the speed be x
800(x-30)=400(x+30)
800x-24000=400x+12000
400x=36000
x=90


800(90-30)=400(90+30)
48000=48000


Hence, the speed of the boats are 90meters per minute and the lake is 4800 meters wide or 48km wide.
Paul.</PRE>