Consider this option:
1. if to re-write the condition, it is given: total time t=8 hours; upstream=downstream=6 miles; V_boat=4 m/h., V_current=V=?
2. note, that total time=time_upstream+time_downstream, where time_upstream=6miles/(V_boat-V) and time_downstream=6miles/(V_boat+V). Using this it is possible to make up and solve the following equation:

answer: √10
P.S. the roots of the equation are √10 and (-√10), only positive values is needed for V.
Step-by-step explanation:
3x + 1 = 5x
Bringing like terms on one side
1 = 5x - 3x
1 = 2x
1/2 = x
They aren't similar because they're not proportional (the sides do not form equal ratios)<span />
Answer: x = 7
Step-by-step explanation: