George box, a famous statistician, once said, "all models are wrong, but some are useful.” what did george box mean by this statement?

Sample answer : a model is an estimate or approximation of a data set. In the real world, there are too many variables to know exactly what will happen. However, if a model is a good fit, then it can be used to make predictions about what will happen. With a useful model, a predicted value should be a good estimate of an observed value.

Basically meaning that no model can exactly be on point with whatever it is modeling. Two things cannot be EXACTLY identical to what they are referring to, but it is saying that some can get close enough to be useful as an example. 

  7/6

Step-by-step explanation:

You have correctly graphed the line, so you know that the rate of change is ...

  ∆d/∆t = 7/6

d changes by 7/6 units for each unit change in t.