How would I graph 5x+3y=-15? How would I graph 8x+2y=-4? Is the x=8/-3 the x-intercept for the equation -3x+4y=8?

One method to graph is to find the x and y intercept of the equation. Then use the intercepts to graph the line.
 
Example 1:  5x+3y=-15
To find the x-intercept of the linear equation let y=0 and solve for the x value.
5x+3y=-15
5x+3(0)=-15
5x=-15
x=-3
Therefore one point on the line is the coordinate (-3, 0).
To find the y=intercept of the linear equation let x=0 and solve for the y value.
5x+3y=-15
5(0)+3y=-15
3y=-15
y=-5
Therefore a second point on the line is the coordinate (0, -5).
Plot the points (-3, 0) and (0, -5) and draw a line through the two points.
 
 
The same method can be used for the second example.
Example 2: 8x+2y=-4
To find the x-intercept of the linear equation let y=0 and solve for the x value.
8x+2y=-4
8x+2(0)=-4
8x=-4
x=-1/2
Therefore one point on the line is the coordinate (-1/2, 0).
To find the y=intercept of the linear equation let x=0 and solve for the y value.
8x+2y=-4
8(0)+2y=-4
2y=-4
y=-2
Therefore a second point on the line is the coordinate (0, -2). Plot the points (-1/2, 0) and (0, -2) and draw a line through the two points.
 
Example 3: -3x+4y=8
To find the x-intercept of the linear equation let y=0 and solve for the x value.
-3x+4y=8
-3x+4(0)=8
-3x=8
x=-8/3
Therefore one point on the line is the coordinate (-8/3, 0). To find the y=intercept of the linear equation let x=0 and solve for the y value.
-3x+4y=8
-3(0)+4y=8
4y=8
y=2
Therefore a second point on the line is the coordinate (0, 2). Plot the points (-8/3, 0) and (0, 2) and draw a line through the two points.