Newton’s law of cooling states that for a cooling substance with initial temperature t0 , the temperature t(t) after t minutes can be modeled by the equation t(t)=ts+(t0−ts)e^−kt , where ts is the surrounding temperature and k is the substance’s cooling rate. a liquid substance is heated to 80°c . upon being removed from the heat, it cools to 60°c in 15 min. what is the substance’s cooling rate when the surrounding air temperature is 50°c ? round the answer to four decimal places. a.) 0.0687 b.) 0.0732 c.) 0.0813 d.) 0.0872