Answer: 
Step-by-step explanation:
We have the following function:

And we have to evaluate it when
, this means we have to substitute
by
:

Solving:

Finally:

Answer:
(-4a + b – 2c) – (3a + 2b –c)
-4a+b-2c-3a-2b+c
-7a-b-c
Step-by-step explanation:
The product of this is 81