The equations are

                         Equation (1)

                    Equation (2)

Multiply the first equation by 4.

         (Distributive property: )

                   (Multiply: )

                       (Multiply: )

                       Equation (3)

 Since the coefficients of the y-terms are additive inverses, y-terms can be

eliminated by adding the equations 2 and 3. 

Write the equations in column form and add the corresponding columns.

Apply division property of equality: if a = b then 

                        (Divide each side by  negative 3)

                                         (Cancel commen terms)

                                    (Divide: )

Now Substitute   in either equation to find the value of y.

       (Equation 1)

                               (Multiply: )

                     (Subtract 4 from each side)

                     (Apply commutative proparty: a+b=b+a)

                                (Apply additive inverse proparty: )

                                (Apply additive identity proparty: )

                                   (Subtract: )

                         (Multiply each side by negative one)

                                              (Product of two same signs is positive)

                                      (Product of two different signs is negative)

The solution is ,.

The solution is .