Find the Indicated Partial Derivative $$f ( x , y ) = x ^ { 2 } y ^ { 4 } - 6 x ^ { 4 } y , f _ { m x }$$

Find the indicated partial derivative.
$$f ( x , y ) = x ^ { 2 } y ^ { 4 } - 6 x ^ { 4 } y , f _ { m x }$$