Substitute in slope formula.

                       (Product of two same signs is positive)

                          (Add: )

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

   (Multiply each side by )

                       (Cancel common terms)

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

                   (Divide each side by negative 4)

                                  (Cancel common terms)

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

                       (Add 6 to each side)

                                  (Apply additive inverse property: )

r = 7                                       (Add: 1 + 6 = 7)

The value of r is 7.