Question 412273
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Hi
Let x and y represent the speed of the jet and wind respectively
Question states*** d = r*t
 7x - 7y = 6440
 3x + 3y = 3780 |multiplying thru with 7/3 to eliminate y

 7x - 7y = 6440
 7x + 7y = 8820
    14x =  15260
      x = 1090mph, speed of jet
      y = (7*1090 - 6440)/7   |substituting into 1st Eq
      y = 170
CHECKING our Answer***
3*1090 + 3*170 = 3780