For this case, the first thing you should observe is that we have a linear equation.
The generic equation of the line in this case is:
d (n) - d (n0) = m (n-n0)
We look for the slope:
m = (d (n2) - d (n1)) / (n2-n1)
m = (560 - 690) / (2-0)
m = -65
Then, we choose any ordered pair:
(n0, d (n0)) = (0, 690)
We substitute the values in the generic equation:
d (n) - 690 = -65 (n-0)
We rewrite:
d (n) = -65n +690
Answer:
A function that represents this situation is:
d (n) = -65n +690
(option 3)