The parabolic arch of a bridge over a one-way road can be described by the equation y = -x^2 + 6, where x and y ar emeasured in metres. a transpor truck is 3m wide and 3.5m high. what is the maximum clearance of the truck's top corners if it passes under the bridge?

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, 

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