Which polynomials are prime? Check all that apply. 15x ^ 2 + 10x - 9x + 7 20x ^ 2 - 12x + 30x - 18 6x ^ 3 + 14x ^ 2 - 12x - 28 8x ^ 3 + 20x ^ 2 + 3x + 12 11x ^ 4 + 4x ^ 2 - 6x ^ 2 - 16