Question 357658
{{{180/r - 180/(r+5) = 1/2}}},
{{{180(1/r-1/(r+5)) = 1/2}}},
{{{360*(5/(r(r+5))) = 1}}},
{{{1800 = r^2+5r}}},
{{{r^2+5r-1800=0}}},
{{{(r-40)(r+45) = 0}}},
Therefore r = 40 miles per hour.