Answer:
Explanation:
part A) is just asking you to add side 1 + side 2
part B) is asking for the third side, since you are given perimeter (sum of all sides) you just need to subtract side 3 - side 1 - side 2
part C) for a polynomial to be closed under addition, it just means two polynomials add up to produce another polynomial, same thing for subtraction. use your results from parts A and B to see whether the polynomials are closed under addition/subtraction