posted by Anonymous .
Gone fishing. Debbie traveled by boat 5 miles upstream to
fish in her favorite spot. Because of the 4-mph current, it
took her 20 minutes longer to get there than to return. How
fast will her boat go in still water
Distance = D = 5 miles
Still water speed = S
current speed = 4 m.p.h.
Time to go upstream,T1 = 5/(S-4)
Time to go downstream, T2 = 5/(S+4)
T1-T2 = 20/60 hour
Can you take it from here?