According to federal tax law, corporations need not pay taxes on 80% of dividends received from shares

Question:

According to federal tax law, corporations need not pay taxes on 80% of dividends received from shares held in other corporations. In other words, only 20% of the dividends received by a corporate holder are taxable. Given this fact, how much must the price of a stock fall on the ex- date in order to prevent a corporate holder from making arbitrage profits? Assume that the capital gains rate equals the corporate tax rate, (c - .5?
Dividend
A dividend is a distribution of a portion of company’s earnings, decided and managed by the company’s board of directors, and paid to the shareholders. Dividends are given on the shares. It is a token reward paid to the shareholders for their...