I am having a hard time understanding factoring and multiplying
polynomials. I have a couple of problems I just can't get, can you
please help me?

Simplify, do not use negatives in the answer:

**(5a**^{-1}b^{-7})(-2a^{4}b^{2})

and:

**(5x**^{2}y^{-7}z)(-4xy^{-3}z^{-4})