A small object with an initial temperature of 135 degrees Fahrenheit is dropped into a tub with a temperature of 60 degrees Fahrenheit. The function f(t) = Ce(kt) + 60 represents the situation, where t is time in minutes, C' is a constant, and k is a constant. After 6 minutes the object has a temperature of 85 degrees. What is the approximate value of k? Round to three decimal places. Provide your answer below: