This is a procedure that you should follow from either your notes or your manual.
Push stat, edit and enter both lists.
Now, go to stat, calc, #4 (LinReg), enter
Push 2nd 1(which is L1), then comma, then 2nd2(which is L2) then enter
You should get the equation
y = ax + b
and the following values for a and b
a = 1.607142857
b = 2.571428571
This is what to do to actually see the line graphed. After L1,L2 above, put a comma then-
Push vars, scroll to y-vars, #1, #1 again.
You should now see L1,L2,Y1(no spaces between entries).
Enter, and graph.