The weekly marginal cost of producing $x$ pairs of tennis shoes is given by the following function, where $C(x)$ is cost in dollars.

$C^{\text{'}}(x)=12+\frac{500}{x+1}$

If the fixed costs are $$3,000$ per week, find the cost function. What is the average cost per pair of shoes if $1,000$ pairs of shoes are produced each week?

The cost function is $C(x)=$