For this case we have the following function: f (t) = -16t2 + 32t + 384 By definition we have to: The average rate of change: AVR = (f (t2) - f (t1)) / (t2 - t1) Where, For t1 = 4 f (4) = -16 * (4) ^ 2 + 32 * (4) + 384 f (4) = 256 For t2 = 6 f (6) = -16 * (6) ^ 2 + 32 * (6) + 384 f (6) = 0 Substituting values we have: AVR = (0 - 256) / (6 - 4) AVR = -128 Answer: The average rate of change of f (t) from t = 4 seconds to t = 6 seconds is -128 feet per second.