I've had a quick look at the maths problem and it's simple enough. Unfortunately I'm on a phone so I may not be able to explain it all that well.
Using speed = distance/time
Time is equal in both instances:
Let x be the wind speed
Using distance1 as 7 miles @ speed1 180+x
And distance2 as 5 miles @ speed2 180-x
distance1/speed1 = distance2/speed2
7/(180+x) = 5/(180-x)
7(180-x) = 5(180+x)
1260 - 7x = 900 + 5x
12x = 360
x = 30 mph