When I should use Substitution, Elimination, or Graphing.

You should use the substitution method when one of the equations have the y or the x value already solved for you or if you just have to take a simple step to find the value because all you have to do is substitute in the y or the x value.
Ex. Y=3x-2.
4x+6y=22. 4x+6(3x-2)=22

You should use elimination method when the y and the x values are lined up both in a standard equation because then, you can add them together like a simple math problem.
Ex. 8x+4y=64 2y=76
-8x-2y=12 Y=38
You should use the graphing method when either all of the equations are in slope-intercept form or when making the equation into a slope-intercept form is faster than doing it another way. You will then put the values into the y= and get the intercepts of the two.
Ex. Y=3x+6 *put in the y-values then press graph. Find the intercept.
2y=5x-1