The answer is 31
It is 31 because all you do is just put the number 6 into the problem and multiply and add it together which will get you 31 minutes to run 6 laps
So check the picture below
if we check the solutions or zeros for the equation, we get

and as you can see in the picture, the value of "x" when y = 3.5, or the height of the truck is

the truck, ends up with a clearance of

on either side, so, the maximum clearance, the truck can have, those two clearances added together,
I believe this would be -10b^2+12b-16
Hope this helps!
1/13.5=5/x.
13.5x5=67.5 then divide that by 1 so yea it anwer is 67.5ft