Question 205884
time = distance / rate
total time is 6 hrs


let s="speed of stream"


[40 / (15 + s)] + [40 / (15 - s)] = 6


multiplying by (15 + s)(15 - s) ___ 600 - 40s + 600 + 40s = 1350 - 6s^2


0 = 150 - 6s^2 ___ 0 = 25 - s^2 ___ s = 5