Question 1189536
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b = speed of the boat in still water
c = speed of the current


When the boat goes upstream, the current slows the boat down to a speed of b-c


For the upstream data, we'll plug in the given distance and time to solve for b
distance = rate*time
343 = (b-c)*7
343/7 = b-c
49 = b-c
49+c = b
b = 49+c


When the boat goes downstream, the current speeds up the boat to a speed of b+c


Plug in the distance and time pertaining to the downstream scenario, along with b = 49+c, to solve for c.


Distance = rate*time
819 = (b+c)*9
819 = (49+c+c)*9
819 = (49+2c)*9
819/9 = 49+2c
91 = 49+2c
2c+49 = 91
2c = 91-49
2c = 42
c = 42/2
c = 21
<font color=red>The speed of the current is 21 km per hour.</font>
b = 49+c
b = 49+21
b = 70
<font color=red>The boat's speed in still water is 70 km per hour.</font>
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