Question 256754
5(r+w)=900 You have got the hard part done already.
7(r-w)=700
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5r+5w=900
7r-7w=700
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7r=700+7w
r=100+w
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5r+5w=900
5(100+w)+5w=900
500+5w+5w=900
10w+500=900
10w=400
w=40 kmph rate of the wind
r=140 kmph rate in still air