Question 415262

let assume the speed of the airplane = x mph

4110/(x+20)  = 330 /(x-20)

=> 137/(x+20) = 11/(x-20) .....  after dividing by 30 

=> 137x - 137*20 = 11x + 11*20

=> 126x = 148* 20 

=> x = 148*20 / 126


 x = 23.49 mph