Answer
a. $\bar C(x) =10+\frac{300000}{x}$
b. $y=10$ dollars
Work Step by Step
a. The total cost of producing $x$ players is $C(x)=300000+10x$; thus the average cost is
$\bar C(x)=\frac{C(x)}{x}=10+\frac{300000}{x}$
b. To find the horizontal asymptote, let $x\to\infty$; we have $y=10$ dollars, which represents the average cost when producing unlimited number of players.