Answer
Coefficient of friction is $0.877$.
Work Step by Step
The formula for the speed is
$s=\sqrt{30fd}$
The given values are
Speed of the car $s=55\; mph$
Length of the skid marks $d=115\; feet$
Substitute all values into the formula.
$\Rightarrow 55=\sqrt{30(f)(115)}$
Simplify.
$\Rightarrow 55=\sqrt{3450f}$
Square both sides.
$\Rightarrow 55^2=(\sqrt{3450f})^2$
Simplify.
$\Rightarrow 3025=3450f$
Divide both sides by $3450$.
$\Rightarrow \frac{3025}{3450}=\frac{3450f}{3450}$
Simplify.
$\Rightarrow 0.8768115942=f$
Round to three decimal places.
$\Rightarrow 0.877=f$.
