Answer:the speed of the barge in still water is 11 mph
the speed of the current is 3 mph
Explanation:
Let x represent the speed of the barge in still water.
Let y represent the speed of the current.
Traveling upstream on the Mississippi River, the barge travels 56 mi in 7 h. This is against the water current. It means that the total speed of the barge would be
x - y mph
Distance = speed × time
Therefore,
56 = 7(x - y)
8 = x - y - - - - - - - - - - - -1
Downstream, it travels the same distance in 4 h. This is in the same direction with the water current. It means that the total speed of the barge would be
x + y mph
Therefore,
56 = 4(x + y)
14 = x + y - - - - - - - - - - - -2
Adding equation 1 and equation 2, it becomes
22 = 2x
x = 22/2 = 11
Substituting x = 11 into equation 2, it becomes
14 = 11 + y
y = 14 - 11 = 3