algebra
posted by Anonymous .
Gone fishing. Debbie traveled by boat 5 miles upstream to
fish in her favorite spot. Because of the 4mph 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/(S4)
Time to go downstream, T2 = 5/(S+4)
Difference,
T1T2 = 20/60 hour
Can you take it from here?