The equations are .

                  Equation (1)

          Equation (2)

Since the coefficient of a is same in both equations, either equation can be used for solution. Solve the second equation for a.

Apply subtraction property of equality: If a = b then a b = b a.

Apply addition property of equality: If a = b then a + b = b + a.

               (Subtract a from each side)

                           (Apply additive inverse property: )

Substitute in equation (2).

Distribute terms using distributive property: .

                       (Add: )

Apply subtraction property of equality: If a = b then a b = b a.

Apply commutative property of addition: .

                     (Apply additive inverse property: )

                           (Apply additive identity property: )

                                   (Subtract: )

Apply multiplication property of equality: If a = b then a b = b a.

                              (Divide each side by 4)

                                     (Cancel common terms)

Substitute in equation .

                                    (Add: 8 + 1 = 9)

The solution is .