Answer: First section: (x³+x²-x-1); Second section: (2x³-6x+4); Total volume: (3x³+x²-7x+3)
Explanation:
The picture I attached was the lines I drew to make finding the volume easier.
To find the second upper side I subtracted x+1 from 2x+3, which came to x+2.
This is why I scrapped out the 2x+3 in the bottom to make it less confusing.
Now you should be able to separate the two prisms.
For the first section, multiply (x+1)(x+1)(x-1). I'll do the right two first because it's easier.
(x+1)(x²-1x+1x-1) -1x and 1x cancel out. So now it's (x+1)(x²-1).
The volume of the first section is (x³+x²-x-1).
For the second section, multiply (x+2)(2x-2)(x-1).
The first two turn out as (2x²-2x+4x-4), which is (2x²+2x-4). Then, multiply all that by (x-1): (2x²+2x-4)(x-1).
You should get (2x³-2x²+2x²-2x-4x+4), which is then (2x³-6x+4).
So the volume of the second section is (2x³-6x+4).
Then it asks you to find the total volume, so just add the two volumes: (x³+x²-x-1) + (2x³-6x+4). Then add like-terms.
(3x³+x²-7x+3) should be the total volume.
For the explaining part (being pretty vague), just say how the volumes for both sections were added by like-terms to sum up to the total volume of the plant stand.
Hope that had helped (or at least worked) :p