What financial reporting component reflects cumulative investments back into the company?

The financial reporting component that reflects cumulative investments back into the company is retained earnings. Retained earnings represent the portion of a company’s profit that is kept in the company rather than distributed as dividends to shareholders. This accumulated profit can be reinvested in the business for expansion, research and development, or paying down debt, among other uses.

When a company generates profits, these are added to retained earnings, thus showing how much of the company’s earnings have been reinvested over time. This accumulation is crucial for assessing the company's ability to self-finance its operations and growth without seeking external financing.

On the other hand, common shares refer to equity investments made by shareholders and represent ownership in the company, but they do not specifically account for cumulative earnings retained. Treasury shares are shares that have been repurchased by the company and are not considered in calculating earnings for reinvestment. Par value is a nominal value assigned to shares and does not reflect actual investment or accumulated profits within the business.

Therefore, retained earnings uniquely encapsulate the cumulative investments back into the company, making it the correct answer in this context.