Answer:
5x^3 -80x = 5x(x -4)(x +4)
Explanation:
The denominator factors are ...
(x -4)(x +4)
x
5(4 -x) = -5(x -4)
The unique factors are 5, x, (x -4), (x +4). The LCD is the product of these:
5x(x^2 -16) = 5x^3 -80x
_____
Additional comment
When expressed over the LCD, the expressions are ...
5x^2/(5x^3 -80x), 20(x^2 -16)/(5x^3 -80x), -8x(x +4)/(5x^3 -80x)