help me please

Continuing from 2ab² - ac +bc -2b³   look at the first and last term: they can be factored as 2b²(a-b).  The other two terms can be factored as -c(a-b), so together we have 2b²(a-b) - c(a-b) which can be further factored as (a-b)(2b² - c).

.

a(2b^2-c)+b(c-2b^3)

=a*2b^2-a*c+b*c-b*2b^2

=2ab^2-ac+bc-2b^3

=2ab^2-2b^3-ac+bc

And there you have it.