on dry asphalt the distance d (in feet) needed for a car to stop is given by d =0.05s^2 + 1.1s where s is the cars speed (in miles per hour). what speed limit should be posted on a road where drivers round a corner and have 80 feet to come to a stop?

I did it this way...why is this way wrong?
80 = .05s^2 + 1.1s
1600 = s^2 +22s (divide thru by .05)
1600 + 121 = s^2 + 22s +121 (compl. sq)
1721 = (s +11) ^2
sqrt (1721) - 11 = s
41.48 - 11 = s
30 mph = s