According to Newton's Law of Cooling, the Temperature $T$ Of a Warm Object Decreases at a Rate Proportional to a Warm

According to Newton's Law of Cooling, the temperature $T$ of a warm object decreases at a rate proportional to the difference between $T$ and the temperature $T _ { o }$ of its surroundings.(a) Write down this law as a differential equation.(b) Assume the room temperature is 70 $^\circ$ F. If it takes 2 minutes for a cup of hot coffee to cool down to 180 $^\circ$ F, and how long it takes to cool a cup of coffee from 200 $^\circ$ F to 100 $^\circ$ F.