Answer:
Since The equation that depicts the motion of the Car is given.
The speed in terms of the tire marks...
s= 2√5x
where x is the tire marks(in feet.)
s is the speed(miles per hr)
We can't use the speed in Miles per hr when the tire mark is feet.
1mile = 5280ft
90miles x 5280ft/1mile = 475,200ft/hr
Making x the subject
x= s/2√5
x= 475/200/(2√5 )
=106,257ft
I still can't see what I'm missing or You sure you didn't forget to add something else to the question?