<PRE><B>Question 954938</B>
s=speed of boat in still water
90mi/(s+6mph)=45mi/(s-6mph) Multiply each side by (s+6)(s-6)
90mi(s-6mph)=45mi(s+6mph)
90s-540=45s+270 Add 540 to each side.
90s=45s+810 Subtract 45s from each side.
45s=810 Divide each side by 45.
s=18 ANSWER: The speed of the boat in still water is 18 mph
CHECK:
90mi/(18mph+6mph)=45 mi/(18mph-6mph)
90 mi/24mph=45mi/12mph
3.75 hours=3.75 mph</PRE>