Answer
rowing in still water: 6.5 mph
rate of the current: 2.5 mph
Work Step by Step
2 hours downriver, 4.5 hours downriver
$18=(x+y)*2$
$18=(x-y)*4.5$
$18=(x+y)*2$
$2x+2y=18$
$18=(x-y)*4.5$
$4.5x-4.5y=18$
$4.5x-4.5y=2x+2y$
$2.5x=6.5y$
$2x+2y=18$
$4.5x-4.5y=18$
$4.5x-4.5y=18$
$2/9*(4.5x-4.5y=18)$
$x-y=4$
$2x+2y=18$
$x-y=4$
$x-y=4$
$2*(x-y=4)$
$2x-2y=8$
$2x+2y=18$
$2x-2y=8$
$2x-2y+(2x+2y)=8+18$
$4x=26$
$4x/4=26/4$
$x=13/2$
$2x-2y=8$
$2*13/2-2y=8$
$13-2y=8$
$5-2y=0$
$5=2y$
$5/2=2y/2$
$y=5/2$
