The partial factorization of x2 – x – 12 is modeled with algebra tiles.Which unit tiles are needed to complete the factorization?

Please write that as x^2 - x - 12 (the "^" symbol denotes exponentiation).

x^2 - x - 12 factors to (x + 3)(x - 4),  Check this by multiplication:

x^2 + 3x - 4x - 12 = x^2 - x - 12 (OK).