If $$f(x, y) = x^{3}y - xy^{3}$$, then what is the value of $$[\frac{1}{(\frac{df}{dx})}+\frac{1}{(\frac{df}{dy})}] x = 1, y = 2 ?$$

A

$$\frac{13}{18}$$

B

$$\frac{-9}{18}$$

C

$$\frac{9}{22}$$

D

$$\frac{-13}{22}$$