The lengths of two sides of a triangle are shown below:

Side 1: 8x^2 - 5x - 2
Side 2: 7x - x^2 + 3

The perimeter of the triangle is 4x^3 - 3x^2 + 2x - 6

Part A: What is the total length of the two sides, 1 and 2, of the triangle?

Part B: What is the length of the third side of the triangle?

Part C: Do the answers for part a and b show that the polynomials are closed under addition and subtraction? Justify your answer.