Rio Tinto is a globally diversified industrial conglomerate, headquartered in London and has an Australian head office in Melbourne. The company's most recent dividend was $5.61, and the company expects to experience rapid growth in dividends for the next two years at the annual rates of 15% and 12% in year 1 and year 2 respectively. After the first two years, Rio Tinto's dividends will grow at an annual rate of 7% in the third and fourth years, and beginning with the fifth year, its dividends are expected to attain a 5% p.a. growth rate which will be sustained thereafter. Rio Tinto's beta is 0.63. The 10-year Australian Government bond yield (bid yield) is 1.74%. The market expected return is 8.90%.

Estimate the shareholders' required rate of return for Rio Tinto share