Question 847758
The current adds to the speed going 
downstream, and subtracts from the speed 
going upstream, so the effect of the 
current cancels to zero
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The total distance is {{{ 36 + 36 = 72 }}} mi
Let {{{ s }}} = the average speed of the
boat relative to the water
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{{{ 72 = s*4.5 }}}
{{{ s = 16 }}} mi/hr