We take any two points to find the slope. Let's choose (-2,9) and (0,10).
Slope=(10-9)/(0+2)=½.
Now let's use (0,10) to find the equation of the line y-10=½x, so y=½x+10.
To prove that we do in fact have a line and not a curve, we can use the equation with all the values of x:
x=-2: y=9; x=0: y=10; x=2: y=11; x=4, y=12 which matches the table.