#### Answer

a. $f(x)=0.1125x^2 - 0.1x + 55.9$
b. $x\gt60\ mph$

#### Work Step by Step

a. The quadratic regression for the dry pavement data is shown in the figure and we get the function as $f(x)=0.1125x^2 - 0.1x + 55.9$
b. Letting $f(x)\gt455$, we have $0.1125x^2 - 0.1x + 55.9\gt455$ or $0.1125x^2 - 0.1x -399.1\gt0$, which can be solved graphically as shown in the figure with solutions of $x\gt60\ mph$