The message 'Please use x and y variables to specify a graph you want to draw​.' means you should type down the functions using 'x' and 'y' so that the solver can graph them.​

Plot the points (0,-4),(-3,0),(-3,1),(-4,1).

Click here to see the graph.

The point:

(0, -4) is in the intersection of the lines 'x = 0' and 'y = -4'

(-3, 0) is in the intersection of the lines 'x = -3' and 'y = 0'

(-3, 1) is in the intersection of the lines 'x = -3' and 'y = 1'

(-4, 1) is in the intersection of the lines 'x = -4' and 'y = 1'