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 

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