Which polynomials are prime? Check all that apply.

15x2 + 10x – 9x + 7
20x2 – 12x + 30x – 18
6x3 + 14x2 – 12x – 28
8x3 + 20x2 + 3x + 12
11x4 + 4x2 – 6x2 – 16