The equation in the problem solves the speed as 48.99 miles per hour. At this speed the car takes 100 feet to stop ( also shown in the equation as they replaced d with 100).
This means any speed below 48.99 miles per hour would stop before hitting the tree.
The fastest the car can go would be 48.98 miles per hour.
Justify by replacing s in the equation with 48.98 and solve for d:
48.98 ^2 = (sqrt( 30(0.8)d)
2399.04 = 24d
D = 2399.04/24
D = 99.96 feet
This is less than 100 feet so the car will not hit the tree.
