Question 1204831
<pre>
                 SPEED      TIME      DISTANCE
GOING TO           r        x+4       9900/2=4950
COMEING BACK       r+50     x         9900/2=4950

</pre>
Note that the variables here were assigned differently than your exercise instructed to do.  x here is time for the return trip and r is for speed of the plane absent of any wind.  Notice, no wind involved for the return trip.
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{{{system(rx+4r=4950,rx+50x=4950)}}}


{{{4950-4r=4950-50x}}}
{{{4r=50x}}}
{{{2r=25x}}}
{{{r=25x/2}}}


substiture r in first equation.
{{{(25x/2)x+4(25x/2)=4950}}}
{{{(25/2)x^2+(4*25/2)x-4950=0}}}

{{{highlight_green(x^2+4x-396=0)}}}


{{{x=(-4+- sqrt(16+4*396))/2}}} must use the positive s.r.

{{{x=(-4+sqrt(16+4*396))/2}}}

{{{x=(-4+sqrt(1600))/2}}}

{{{x=(-4+40)/2=-2+20=22}}}--------{{{highlight(x=22)}}}------Time hours for the return trip.
Therefore {{{r=25x/2}}}
{{{r=25*22/2=25*11}}}
{{{highlight(r=275)}}}---------speed of plane if no wind


TIME for total round trip, {{{22+4+22=highlight(48*hours)}}}