How do I solve a simultaneous equation?

In a simultaneous equation, you have tow unknown constants. For example: 2x + y = 18; x − y = 6. To find out the values of each, you first need to find one. You do this by getting one constant on its own on one side of one equation: x - y = 6 can be changed to x = y + 6. This can be rewritten as x = (y + 6). This shows that x is the same as y + 6, so hopefully you can see how we can now plug in this expression into the OTHER equation: 2x + y = 18 can be rewritten as 2(y + 6) + y = 18. We can now solve this.2y + 12 + y = 183y = 6y = 2We can now plug the value of y into either equation to find x.x - y = 6x - (2) = 6x = 8