A pan of water is brought to a boil and then removed from the heat. Every 5 mins thereafter the difference between the temperature of the water and...

A pan of water is brought to a boil and then removed from the heat. Every 5 mins thereafter the difference between the temperature of the water and room temperature is reduced by 50%.

1) Room temperature is 20 degrees Celsius. Express the temperature of the water as a function of the time since it was removed from the heat.

2)How many times does it take for the temperature of water to reach 30 degrees celcius