Given equation is .

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

          (Add 3y to each side)

Rearrange the terms using commutative property of addition: a + b = b + a.

                   (Apply additive inverse property: )

                         (Apply additive identity property: )

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

         (Subtract 18 from each side)

                  (Apply additive inverse property: )

                        (Apply additive identity property: )

Apply division property of equality:If then .

                    (Divide each side by 3)

                        (Cancel common terms)

                      (Simplify)

                           (Divide:  )

.

The option "C" is correct.