Ineed the answer to 5+ bracket 2 times bracket 14 minus 9 bracket minus 1

5+2x14-9-1
5+28-9-1
38-9-1
29-1
28

1. For the total length of the two sides, you have to add the two polynomials together:


We can just combine like terms and we have our


2. We can set it up as:


All we need to do is subtract the polynomials to solve for y:


Simplify (subtract like terms):


That's the length of the 3rd side!

3. Yes, you can say that polynomials are closed under addition and subtraction based on Part A and Part B because whenever you add/subtract polynomials, you get an element from the same set. Indeed, they are 'closed'. 

Hope my answer helped! :)