When you sum two algebraic expressions, you simplify like terms (terms with variable of the same order).
Then, for the given expression you obtain:
x^5 + 2x^3 + 2x^2 + 6x + 3
-3x^5 - 3x^4 + 2x^3 + 6x
-2x^2 - 3x^4 + 4x^3 + 2x^2 + 12x + 3
Hence, the result of the sum of the given expression is:
-2x^2 - 3x^4 + 4x^3 + 2x^2 + 12x + 3