You have entered the following equation

x + 2y = 8

If you want to solve for "x" you need to select solve for "x"

The solution for "x" is

x = -2y + 8

If you select solve for "y" you will get the following solution

y = (-x + 8)/2

y = -x/2 + 4

You can also graph the equation "x + 2y = 8" by simply selecting the "Graph" tab and clicking on "Solve":

Click here to see the graph