Electronics manufacturer Electric$-$X found that the average cost $C$ to produce $$ DVD$/$Blu$-$ray players can be found using the equation

$C=0\mathrm{.}03x^2-5\mathrm{.}04x600$

Use the equation to find how many DVD$/$Blu$-$ray players Electric$-$X should build in order to minimize cost and what is the minimum average cost.

a$.$ The number of DVD$/$Blu$-$ray players that Electric$-$X should build to minimize cost is:

b$.$ The minimum average cost is: $$ dollars