Looking at the data we can see that everytime "x" goes up by 1 the rate of change in "y" is -3. The function also appear to be changing in a linear fashion, therefore we can use a formula such as:
y = a*x + c
Since tha rate of change is -3, then a = -3:
y = -3*x + c
Applying the equation above to a few points must give us the value for c:
