how can i decompose this partial fraction(4x^3)/(x^3-x^2)

This is not a "proper" decomposition problem. Typically the degree of the denominator is greater than the degree of the numerator...

but...we can still simplify...
notice that this expression can be factored:

from here we notice that by polynomial long division (don't know how to show using this editor) that:

so our expression simplifies to...



:)