I don't know how to simplify this:

4ab^2(-3a^2b)^2/ (-2ab)^3

Just apply the laws of exponents. When you multiply exponent terms, you add the exponents. When you divide, you subtract the exponents.

\frac{4ab^{2}(-3a^{2}b)^{2}}{(-2ab)^{3}}

=\frac{36a^{5}b^{4}}{-8a^{3}b^{3}}

Now, you try finishing. Remember the rule about dividing exponents... subtract the exponents. Just make sure you keep like terms together. That is, you can't divide \frac{a^{5}}{b^{3}}. Keep the a's with the a's and the b's with the b's.

ohhh.
so would the answer be 4.5a^2b ?

Yes, it would. :)

Except you forgot a negative. Perhaps write the 4.5 as 9/2

Good work. See, you can do it.