Answer
$6.2$ mph.
Work Step by Step
Distance traveled = (average speed)(time of travel).
Let $x$ mph be the wind speed.
Against the wind, the average speed is $(180-x)$ mph, and time =3 h,
so distance = $3(180-x)$ miles.
With the wind, the average speed is $(180+x)$ mph, and time =$2.8$ h,
so distance = $2.8(180+x)$ miles.
The distances discussed are equal.
$3(180-x)=2.8(180+x)$
$ 540-3x=504+2.8x\qquad$ ... add $3x-504$
$36=5.8x$
$x=\displaystyle \frac{36}{5.8}\approx 6.2$
The wind speed is $6.2$ mph.
