2x + y = 18; x−y=6

This is an an example of simultaneous equations, no single equation can give us the answer. Were going to use the substitution method. We will call this equation 1: 2x + y = 18, and this equation 2: x-y=6. Adding +y to both sides of equation 2, we get: x-y+y=6+y, simplified: x=6+y. Now this is great as we now have a definition for x alone. Substituting our definition for x into equation 1 we now have: 2( 6+y)+y=18. Simplifying we get: 12+2y+y=183y=18-12y=6/3=2using our definition of x from earlier x=6+2=8