7)  Rate Function is Y=.04(T)-.9

Y=.02(4)^2-.9(4)+12

Y=.32-15.6   

Y=-15.28 

Y=.02(12)^2-.9(12)+12

Y=2.88-22.8=-19.64

 The rate function that a person would use to solve this problem is rate =change in Depth / change in Time

 Finding the midpoint of the two interval will give you a more accurate reading between each  interval.                                                                                                                                                                                                                                                                                                                                                         

The two answers I found compare because the closer the readings are between each interval the less room you have for error.