The range is the interval of y values.
Smallest y values is -9 and the highest y values is 9.
So the range is
Let's call the number you thought of n. Then what the two steps you took can be written as an equation:

Subtract n to get all of your variables to one side:

At this point, I recommend turning your mixed number into an improper fraction. It will make things easier later on:

Now divide both sides by 11 to get the value of n:
Answer:
the answer I got was 2878.3
Answer:
We can use excel regression data analysis tool to find the equation of the regression line that best fits the data.
The excel output is attached here.
Therefore, the equation of the linear regression is:

Where:
21.9028 is the intercept and 1.5736 is the slope.