After you have entered the data from section 10
First, we need the value of the slope in cell B15:
In cell A15 enter the label slope
Go to cell B15:
Click on Formula
Click on Paste Function
Click on statistical (under Function Category)
Click on SLOPE (under Paste Function)
Highlight the Y range (A3-A12)
On edit line highlight known_x's
Highilight the X range (B3-B12)
Click in another cell

Now we need the value of the Y intercept in cell B16:
In cell A16 enter the label intercept
Go to Cell B16:
Follow the steps above, except choose INTERCEPT, rather than slope

A formula for predicted Y values needs to be entered into column C:
Type the label Predicted Y in cell C2
Go to Cell C3 and enter the formula:
= ($B$15*A3) + $b$16
Fill the formula down through cell C12

You have now entered a formula for the best fit line. You can proceed with the graphing described in section 10.