# Calculus all the way

**Calculus**Level pending

If Newton's Law of cooling states that the rate at which the temperature of a substance changes is proportional to the difference between the temperature of the object and the surrounding, then what is the time taken for a cup of coffee brewed at 90 degrees celsius at room temperature (20 degrees), to have temperature of 65 degrees celsius? \(constant of proportionality = 0.01 s^{-1} \) Answer in 2 decimal places