A chemist measures the temperature in degrees Fahrenheit of a chemical compound every hour. The temperatures approximate a geometric sequence where an is the temperature at a given hour, and n is the hour. At hour 4, the temperature is 60 °F and at hour 6, the temperature is 68 °F . Use a calculator and round the temperature at hour 1 to the nearest degree, otherwise round decimal numbers to the nearest hundredth if necessary. The explicit rule for the geometric sequence is an =___(___)^n − 1.