Here's the question you clicked on:
786889
cost function :the weekly marginal cost of producing x pairs of tenis shoes is c'(x)=12+500/x+1 where c(x) is cost in dollars if the fixed costs are 2000 per week find the cost function what is average cost pe pair of shoes if 1000pairs of shoes are produced each week
I won't do it for you but I will tell you how. They are asking for the average cost per pair of shoes which is equal to the total cost divided by the number of shoes produced. You have to get total cost and you have the marginal cost. They gave you the fixed cost. It's simple mathematics now.