Question 727285
Let {{{ c }}} = the speed of the current
The time, {{{ t }}} is the same for both trips
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The speed going downstream minus the speed of the current 
equals the speed going upstream plus the speed of the current
{{{ 8/t  - c = 4/t + c }}}
{{{ 2c = 8/t - 4/t }}}
{{{ c = 4/t - 2/t }}}
{{{ c = 2/t }}}
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