The given expression is a product of two binomials, (x - 4) and (x + 5). To find the product, we can use the FOIL method, which stands for First, Outer, Inner, Last. Multiplying the first terms of each binomial gives us x * x = x^2. Multiplying the outer terms gives us x * 5 = 5x. Multiplying the inner terms gives us -4 * x = -4x. Multiplying the last terms gives us -4 * 5 = -20. Combining like terms, we get x^2 + 5x - 4x - 20, which simplifies to x^2 + x - 20. Therefore, the correct answer is x^2 + x - 20.