Question 1066873
r, the speed of the eastward bound plane


North leg distance
{{{(r+50)*3}}}


East leg distance
{{{r*3}}}



{{{(3r+150)^2+9r^2=2320^2}}}


{{{9r^2+900r+22500+9r^2=2320^2}}}


{{{18r^2+900r+22500-5382400=0}}}


{{{18r^2+900r-5359900=0}}}


{{{9r^2+450r-2679950=0}}}


{{{r=(-450+sqrt(450^2+4*9*2679950))/18}}}


{{{r=(-450+sqrt(96680700))/18}}}


{{{r=(-450+10*sqrt(966807))/18}}}


{{{r=(-450+30*sqrt(107423))/18}}}


{{{r=(-75+5*sqrt(107423))/3}}},   17*71*89 is the discriminant factored.


{{{highlight(r=84)}}}