A cup of hot coffee is placed on a desk in a room with ambient temperature 20°C. The coffee's temperature follows Newton's Law of Cooling: $T(t) = 20 + Ce^{-kt}$, where $T$ is temperature in Celsius and $t$ is time in minutes. Initially, the coffee is at 80°C. After 10 minutes, its temperature drops to 50°C. What will be its temperature after 20 minutes (to the nearest degree)?