Explain in words why new common stock that is raised externally has a higher percentage cost than

Question:

Explain in words why new common stock that is raised externally has a higher percentage cost than equity that is raised internally as retained earnings.

Common Stock
Common stock is an equity component that represents the worth of stock owned by the shareholders of the company. The common stock represents the par value of the shares outstanding at a balance sheet date. Public companies can trade their stocks on...