Remember that 
. Since the distance of the complete trip is 312 miles, the distance of each way is 
miles.
Let
be the speed of the boat in still water and 
the speed of the current.
Now, for the downstream trip the boat is traveling with the current, so:
this will be our equation (1)
For the trip back the boat is traveling against the current, so:
this will be our equation (2)
Next, lets add equation (1) and equation (2) to get rid of
:
Finally, now that we know the speed of the boat in still water, lets replace that value in our equation (1) to find the speed of the current:
We can conclude that the speed of the boath in still water is 9
, and the current of the stream is 3.
Let
Now, for the downstream trip the boat is traveling with the current, so:
For the trip back the boat is traveling against the current, so:
Next, lets add equation (1) and equation (2) to get rid of
Finally, now that we know the speed of the boat in still water, lets replace that value in our equation (1) to find the speed of the current:
We can conclude that the speed of the boath in still water is 9
