Answer: Option 'D' is correct.
Explanation:
Since we have given that
There is supply and demand graph for MP3 players.
If the price is at the equilibrium point, then at that point of intersecting , we can get our equilibrium quantity too.
There is equilibrium price at $ 55. and from the intersecting point, we get our equilibrium quantity i.e. 60 units.
So, Total cost that the store maker will make by selling MP3 players is given by

Hence, Option 'D' is correct.