The mass of a growing cyst at clock time t is given by m = .05 * t³, where m is mass in grams and t is clock time in months.

• At what average rate is the mass changing between clock times t = 19.9 and t = 20 months? 
• At what average rate is the mass changing between clock times t = 19.9 and t = 19.91 months? 
• At what average rate is the mass changing between clock times t = 19.9 and t = 19.901 months? 
• What do you estimate is the rate at which mass is changing at clock time t = 19.9 months?

The rate at which the mass of the cyst changes is given by Rate = .013 * t², where Rate is rate of change in grams per month and t is clock time in months.  How much do you think mass will change between t = 19.9 and t = 39.8 months?