Cecelia studied for the SAT for 20 minutes every day in the first week, 30 minutes in the second week, 40 minutes in the third week, and 50 minutes in the fourth week. Christopher studied for the SAT for 5 minutes every day in the first week, 10 minutes in the second week, 20 minutes in the third week, and 40 minutes in the fourth week. Which statement best describes the methods used by Cecelia and Christopher to increase the time they spent studying? Cecelia's method is exponential because the number of minutes increased by an equal number every week. Christopher's method is exponential because the number of minutes increased by an equal factor every week. Both Christopher's and Cecelia's methods are linear because the number of minutes increased by an equal factor every week. Both Christopher's and Cecelia's methods are linear because the number of minutes increased by an equal number every week.