Question 881775
Let {{{ s }}} = the speed of the boat in still water
Let {{{ c }}} = the speed of the current
{{{ s + c }}} = the speed of the boat going downstream
{{{ s - c }}} = the speed of the boat going upstream
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Going downstream:
(1) {{{ 78 = ( s + c )*3.25 }}}
Going upstream:
(2) {{{ 72 = ( s - c )*7.2 }}}
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This is 2 equations with 
2 unknowns, so it's solvable