Question 402051
{{{5/(r - 5) = 15/(r+5)}}}
==> {{{1/(r - 5) = 3/(r+5)}}}
==> r + 5 = 3(r-5)
==> r + 5 = 3r - 15
==> 20 = 2r
==> r = 10 mph, the speed of the boat in still water.