The average daily temperature, t, in degrees Fahrenheit for a city as a function of the month of the year, m, can be modeled by the equation graphed below, where m = 0 represents January 1, m = 1 represents February 1, m = 2 represents March 1, and so on. If the equation is t = a cosine (StartFraction pi Over 6 EndFraction (m + 1)) + k, what are the values of a and k?