At time t=0 minutes, the temperature of a cup of coffee is 180 degrees fahrenheit. Left in a room whose temperature is 70 degrees Fahrenheit, the coffee cools so that its temperature function T(t), also measure in degrees Fahrenheit, the differential equation dT/dt = -1/2T + 35

a) Find an expression for T(t) using the initial condition T(0)=180

c) At what time t is the temperature of the coffee decreasing at the rate of 15 degrees Fahrenheit per minute? How hot is the coffee at that point? Indicate units of measurement.