Okey, here we have the following function:
[tex]C(x)=0.5x^2-260x+53298[/tex]
Considering that "a" is a positive coefficient, then it achieves the minimum at:
[tex]x=-\frac{b}{2a}[/tex][tex]\begin{gathered} x=-\frac{(-260)}{2(0.5)} \\ =\frac{260}{1} \\ =260 \end{gathered}[/tex]
Now, let's find the minimal value of the quadratic function, so we are going to replace x=260, in the function C(x):
[tex]\begin{gathered} C(260)=0.5(260)^2-260(260)+53298 \\ C(260)=0.5(67600)-67600+53298 \\ =33800-67600+53298 \\ =19498 \end{gathered}[/tex]
Finally we obtain that the number of cars is 19498.