Answer
$6a^2b^2-5a^3b^3+ab^3-a^2b$
Work Step by Step
We remove the parentheses, distribute, and then add the products as follows
$$
ab^2(2a - 3a^2b + b) - a^2b(1 + 2ab^2 - 4b)\\
=2a^2b^2-3a^3b^3+ab^3-a^2b-2a^3b^3+4a^2b^2\\
=6a^2b^2-5a^3b^3+ab^3-a^2b
.$$
