Find the Integrating Factor of the Differential Equation $\left( - 14 y ^ { 3 } + 2 \right) d x + \left( 21 x y ^ { 2 } + 7 x ^ { 3 } \right) d y = 0$

Multiple Choice

Find the integrating factor of the differential equation $\left( - 14 y ^ { 3 } + 2 \right) d x + \left( 21 x y ^ { 2 } + 7 x ^ { 3 } \right) d y = 0$ that is a function of $x$ or $y$ alone.

A) $- \frac { 21 } { x }$
B) $- \frac { 3 } { x }$
C) $\frac { 1 } { x ^ { 21 } }$
D) $\frac { 1 } { x ^ { 3 } }$
E) $\frac { 1 } { x ^ { 14 } }$