If the expression start fraction, start root, start index, 4, end index, 16, x, cubed, y, to the power 4 , end root, divided by, x, start superscript, minus, start fraction, 5, divided by, 4, end fraction, end superscript, y, cubed, end fraction x − 4 5 ​ y 3 4 16x 3 y 4 ​ ​ is written in the form a, x, to the power b , y, to the power c ax b y c , then what is the product of a, commaa, bb and cc?