A hot brick is removed from a kiln at 225 C above room temperature. Over time, the brick cools off. After 2 hours have elapsed, the brick is 30 C above room temperature. Let t be the time in hours since the brick was removed from the kiln. Let y = H(t) be the difference between the brick's and the room's temperature at time t: Assume that H(t) is an exponential function. Interpret the physical meaning of the horizontal asymptote of H(t).