The Celsius temperature of a hot potato placed in a room is given by the function T = 51* 2- .0094 t + 17 , where t is clock time in seconds and T is temperature in Celsius.  

The rate at which the Celsius temperature of a hot potato placed in a room is given by Rate = .039 * 2- .0094 t, where R is rate of change in Celsius degrees per second and t is clock time in seconds.  How much temperature change do you estimate would occur between t = 7.5 and t = 15 seconds?