Bob is cooking a roast. The table below gives the temperature R (t) of the roast (in degrees Celsius), at a few tim (in minutes) after he removed it from the oven. Time t (minutes) Temperature R (t) (C) 0 226.6 10 205.6 30 157.6 50 119.6 70 61.6 C (a) Find the average rate of change for the temperature from 0 minutes to 30 minutes. C per minute (b) Find the average rate of change for the temperature from 50 minutes to 70 minutes. C per minute A