Newtons law of cooling says that the temperature of a body changes at a rate proportional to the difference between its temperature and that of the surrounding medium (the ambient temperature), =(), where T is the temperature of the body, t is time, k is the proportionality constant, and Ta is the ambient temperature.

(1) Suppose that a cup of coffee originally had a temperature of 70C. Use Eulers method to compute the temperature from t=0 to 10 min using a step size of 2 min if Ta=20C and k=0.02/min. Present your calculations carefully.

I got the answer, but how can got the value of step 1:69.40C