<PRE><B>Question 914299</B>
I presume it is 7.5 km each way and total time is 3 hours

let current speed = x

7.5/(10+x) +7.5/(10-x) = 3

(7.5(10-x)+7.5(10+x))/((10+x)(10-x)) = 3


(7.5(10-x)+7.5(10+x))=((10+x)(10-x))* 3


75-7.5x+75+7.5x= 3(100-x^2)

150= 300-3x^2

3x^2=150

x^2= 150/3
x^2=50

x=5sqrt(2) km/h



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