If you are plotting the points/line and demonstrating the slope on a graph, then the previous answer is correct. You can set up a table.

However, like the previous answer suggests, the equation must be in slope-intercept format, which is y=mx+b. Since you have x = -4y, you have to do a little simple algebra to flip it around.

If x= -4y
Divide by -4 on both sides.
You get x/-4 = y OR y=x/-4, which is now in slope-intercept format.
The slope (m) is found in front of x and since x/-4 is the same as -1/4x, then you have a slope of -1/4.
This can be seen in the previous post's table. When y (rise) equals -1/2, x (run) = 2. Rise/run = -1/2 /2, which also equals -1/4.

Basically, you can set up a table to solve for the y value.  You pick the x value.

x | y

0 | 0

1 | -1/4

2 | -1/2

Then you can plot these points on your graph.

Using the slope-intercept formula: y = mx + b You can then determine the slope of the line. Remember rise/run.