Answer: x > 0, x = 12 miles per hour
Step-by-step explanation:Let x = speed of boat in still water
Speed upstream (against current) = x-4
Speed downstream (with current) = x+4
Distance = (Rate)(Time), so Time = Distance/Rate
Time upstream + Time downstream = 3
16/(x-4) + 16/(x+4) = 3
16(x+4) + 16(x-4) = 3(x+4)(x-4)
32x = 3(x2 - 16)
3x2 - 32x - 48 = 0
(3x + 4)(x - 12) = 0
x = -4/3 or x = 12
Since x > 0, x = 12 miles per hour