Answer: 4 ( 9 - c ) = 2 ( 9 + c )
Step-by-step explanation:
Since, Distance = Speed × Time
Here c represents the speed of current,
Thus, if the boat has the speed of 9 mph in still water,
Then its speed in upstream = ( 9 - c ) mph
Also, It takes the boat 4 hours to travel upstream.
Hence, total distance in upstream = 4 ( 9 - c )
Similarly its speed in downstream = ( 9 + c ) mph
Also, It takes the boat 2 hours to travel downstream.
Hence, total distance in downstream = 2 ( 9 + c )
Since, the distance in upstream and downstream is equal.
⇒ 4 ( 9 - c ) = 2 ( 9 + c )
Which is the required equation for finding the speed of current c..
