Answer:
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against the wind, an airplane travels 3640 km in 7 hours.
with the wind, the same plane travels 6000 km in 6hrs.
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let speed of plane in still air be x mph
speed of wind be y mph.
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t=d/r
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against wind speed = x-y mph
with wond speed = x=y mph
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3640/(x-y)=7
3640 = 7x-7y
/7
520=x-y.....................1
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6000/x+y = 6
6000 = 6x+6y
/6
1000=x+y.....................2
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Add (1) & (2)
2x=1520
/2
x=760 mph speed of plane in still air
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plug value of x in 2
1000=760+y
100-760=y
240 = y
240 mph speed of wind