Question 1207762
An air rescue plane averages 300 miles per hour in still air. It carries enough fuel for 5 hours of flying time. If, upon takeoff, it encounters a head wind of 30 mi/hr, how far can it fly and return safely? (Assume that the wind remains constant.)

Speed of plane in still air 300 mph
Head wind = 30 mph

Fuel  available for 5 hours 
It means  the plane can fly a total distance of 5*300= 1500 miles (to & fro)
Tail wind  when returning 30 mph

x/(300-30) + x/(300+30)= 5

x/270+x/330 =5

11x/(11*270 )+ 9x/(9*330)=5

(11x +9x)/2970 =5

20x = 14850

x = 742.50  

The plane can fly 742.5 miles one way and then return safely, in the given conditions