Question 704411
This is kind of a trick question, but really, it's supposed
to make you think. When you travel 22.5 miles against
the current, and then back the current opposes you one way
and assists you the other way, so the effects cancel.
So, the operators time on a lake with no current is the same
as the time going up and down the river.
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Let {{{ s }}} = the speed of the boat on the lake
{{{ s = ( 2*22.5 ) / 9 }}}
{{{ s = 45 / 9 }}}
{{{ s = 5 }}} 
He needs to go 5 mi/hr on the lake for the 
boat to work on the river also