system help: How to solve system of equations? - Help.com

By graphing. You draw the graph of each of the equations on the same axes. The point of intersection of the lines is the solution to the equations (x,y).

For substitution, rearrange one or both of theequations (depending on which one is easier to solve) for y or x. And then substitute the whole of that expression in to the other equation and solve. For example;
3x + y = 11
y = 11 - 3x

Put this into the second equation
x + 2y = 12
x + 2(11-3x) = 12
x + 22 -6x = 12
x = 2 and then put this back into the first reaaranged equation;
y = 11 - 3(2)
y = 5
Solution is (2,5)

For the addition method. Add (or subtract the two whole equations;
4x + y = 15
+ -4x +3y = -19
= 0x + 4y = -4
So y = -1 and then put this back into the original equation for x
4x + (-1) = 15
So x = 4
Solution is (4,-1)

Multiply the whole of the second equation by a factor, so that either the coefficient of x or y is the same as the first but of oppisite sign. In this case for example, multiplying the second equation by -2 gives 6y = -4x + 6 and then you can add as before.
(If it makes it easier for you, you can rearrange this equation to -4x = 6y - 6)