Question 28909
His speed of the stillground = 5mph 
Let the speed of the wind be x
Equation:
{{{10/(5+x)=7/(5-x)}}}
Cross multiply:
7(5+x)=10(5-x)
35+7x=50-10x
17x=15
x=0.88 (rounded)


Hence, the speed of the wind is 0.88mph.
Paul.