The equations are

                               (Equation (1)

                                 (Equation (2)

Solve the equation 2 for variable c in terms of the variable d.

Apply subtraction property of equality; if a = b, then .

                (Subtract 3d from each side)

                                  (Apply additive inverse property: )

Substitute for c in equation 1.

Distribute terms using distributive property: a(b – c) = ab – ac.

                    (Multiply: )

                            (Add:)

Apply subtraction property of equality; if a = b, then .

     (Subtract 40 from each side)

          (Subtract: 10 – 40 = - 30)

                        (Apply additive inverse property: 40 40 = 0)

Apply division property of equality: if a = b, then.

                   (Divide each side by negative 10)

                             (Cancel common terms) \ \

                                       (Divide: )

Substitute for d in .

                              (Multiply: )

                                       (Subtract: )

The solution is (1, 3).