Question 63032
[-4ax]/[y + 6a^3a^-2y^-1] / [x - 5y^-1a^-3] / [a^-4x^-1]

=[-4ax]/[y + 6ay^-1] / [x - 5y^-1a^-3] / [a^-4x^-1]
Invert the denominator and multiply as follows:

=[-4ax]/[y + 6ay^-1]*[a^-4x^-1]/[x-5y^-1a^-3]
=[-4ax*a^-4x^-1]/[(y+6ay^-1)(-5y^-1a^-3+x)]
=[-4a^-3]/[-5a^-3+xy-30a^-2y^-2-x]

Comment:
This is a messy problem that strains your eyes and teaches you nothing.
Cheers,
Stan H.