An investor bought $110$ shares of stock at a cost of $$$$9$ per share. He held the stock for $15$ years and then sold it for a total of $$$$3$ comma $960.$ For the first three $$years$,$ he received no dividends. For each of the next seven $$years$,$ he received total dividends of $$$$40$ per year. For the remaining$$ period, he received total dividends of $$$$80$ per year. What rate of return did he make on the$$ investment?