The depth of water in a certain nonuniform container is y = .015 t⁴ + -2.4 t² + 80, where depth y is in cm when clock time t is in seconds.

• At what average rate is the depth of water changing between clock times t = 21 and t = 21.1 seconds?
• At what average rate is the depth of water changing between clock times t = 21 and t = 21.01 seconds?
• At what average rate is the depth of water changing between clock times t = 21 and t = 21.001 seconds? 
• What do you estimate is the rate at which water depth is changing at clock time t = 21 seconds?

The rate at which water flows from a certain nonuniform cylinder is given by rate = .015 t³ + -2.4 t cm³ per minute, where t is in minutes.  How much do water do you think will flow between clock times t = 21.1 minutes and t = 42 minutes?