Graph: `x + y<= 4`
First, graph as line: `x + y = 4 => y = -x + 4`
As a line, y = -x + 4, indicates the slope is -1 and the y-intercept is 4.
Since the inequality is equal as well as less than, graph the line solid.
Use a test point (0,0). Any point will work, however (0, 0) is the easiest.
`0 + 0<=4` Since this is true (0,0) is a solution, therefore shade below the line of y = -x + 4.