An environmentalist reports that the depth of the water in a new reservoir is approximated by
![1490_32ffdfde-f634-4f08-94e7-c4cea6b06fa5.png](https://secure.tutorsglobe.com/CMSImages/1490_32ffdfde-f634-4f08-94e7-c4cea6b06fa5.png)
where t is in weeks since the date the reservoir was completed and h is in meters.
(a) During what period was the reservoir filling at a constant rate? What was that rate?
(b) In this model, is the rate at which the water level is changing defined for all times t > 0? Explain.