Paper and Pencil Solution on the Calculator:
If you prepare your scatter plot on the Graphs & Geometry page, you can examine "your own" line of best fit on the calculator including its equation. After you enter your data ....
From HOME, choose #2 Graphs&Geometry. From MENU, choose #3 Graph Type and #4 Scatter Plot, as seen at the right.
Hit ENTER. 


At the bottom of the screen, highlight the box naming the set to be used for the xvalues, click, and choose "fat". Use your TAB key to highlight box if needed. Do the same for the y set and choose "cal". 



From MENU, choose #4 Window and #9 Zoom Data, to set the window for the plot.
Hit ENTER. 

In the graph at the right, the Entry Line was hidden to allow for a full view of the graph.
To hide entry line:
CTRL G
or MENU, View,
#6 Entry Line




As we did with pencil and paper, choose two points that you think will be on the "bestfit" line. Perhaps you choose again the points
(9, 260) and (30, 530). Different people may still choose different points.


From this screen,
choose
MENU,
#6 Points & Lines,
#4 Line



Move the pencil to the first point
of your choice (9,260). Enter. 
(Should you make a mistake, use CTRL  ESC
to undo the mistake.) 
Move the pencil to the first point
of your choice (9,260). Enter. 
Now, get the equation of the line:

Highlight the line. Hit MENU. #1 Action,
#6 Coordinates and Equations 
Read the equation.

Drag the equation so it can
be clearly seen. 