Question 29434
With the wind = x+30
Against the wind = x-30


<font color = brown>Equation:</font>
{{{720/(x-30)+720/(x+30)=10}}}
{{{720((x-30)+(x+30))=10((x-30)(x+30))}}}
{{{720(2x)=10(x^2-900)}}}
{{{1440x=10x^2-9000}}}
{{{10x^2-1440x-9000}}}
{{{x^2-144x-900=0}}}
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 
{{{x=(-(-144)+-sqrt((-144)^2-4*1*-900))/(2*1)}}}
simplfy, you get two solutions:


x=-6 and x=150


Remove the negative.
Hence, the speed of the plane is 150mph.
Paul.