Question 115726
D=RT 
T=D/R
10=720/(R-30)+720/(R+30) COMBINE THE FRACTIONS USING THE COMMON DENOMINATOR:
(R-30)(R+30) 
10=[720(R+30)+720(R-30)]/(R-30)(R+30)
10=(720R+21600+720R-21600)/(R^2-900)
10=1440R/(R^2-900) CROSS MULTIPLY
10(R^2-900)=1440R
10R^2-1440R-9000=0
10(R^2-144R-900)=0
10(R-150)(R+6)=0
5-150=0
R=150 ANSWER FOR THE SPEED OF THE AIRPLANE.
PROOF
10=720/(150-30)+720/(150+30)
10=720/180+720/120 
10=4+6
10=10