1. A dog eats her food out of a square based rectangular prism with both lengths and width of 15cm and a height of 10cm. As soon as the box is totally empty, a machine automatically refills it at a rate of 3cm^3/s. Find the rate of change of the height of the food within the box 2 seconds after it begins filling.

Okay, I know how to do most of this question, the only thing im confused about is what to do with the time = 2s... Any help would be great, thanks.