Chapter 2.3, Problem 19P

Newton’s law of cooling states that the temperature of an object changes at a rate proportional to the differnce beetween its temperatureand that of its surroundings. Suppose that the tempreture of a cup of coffee obeys Newton’s law of cooling. If the coffee has a temperature of ${200}^{\circ }F$ when freshly poured, and $1$ min later has cooled to ${190}^{\circ }F$ in a room at ${70}^{\circ }F$, determine when the coffee reaches a temperature of ${150}^{\circ }F$.