It is a parallelogram, because it has 2 sets of parallel lines. The top and bottom are parallel to eachother and the side lines are parallel to each other.
For this case we have the following functions:

By definition of composition of functions we have:

Then substituting:

So:

Answer:

Answer: 
============================================
Work Shown:

---------------
Explanation:
The idea is to first get all the y terms to one side. I did this by subtracting 2y from both sides in the third step.
Then factor out y and divide both sides by (8x-2)
Afterward there's the optional steps of simplifying (as shown in the final two steps).
It took them 4 days to install 480 chairs which means if they were working at a constant rate they got 120 chairs installed daily. with 360 chairs left that means in 3 days they will finish. so overall, it took the workers 7 days to finish, or a week.