To simplify this expression we can multiply the two terms together. To multiply these two terms you multiply each individual term in the left parenthesis by each individual term in the right parenthesis.
#(color(red)(x) - color(red)(4))(color(blue)(x^2) + color(blue)(3x) + color(blue)(2))# becomes:
#(color(red)(x) xx color(blue)(x^2)) + (color(red)(x) xx color(blue)(3x)) + (color(red)(x) xx color(blue)(2)) - (color(red)(4) xx color(blue)(x^2)) - (color(red)(4) xx color(blue)(3x)) - (color(red)(4) xx color(blue)(2))#
#x^3 + 3x^2 + 2x - 4x^2 - 12x - 8#
We can now group and combine like terms:
#x^3 + 3x^2 - 4x^2 + 2x - 12x - 8#
#x^3 + (3 - 4)x^2 + (2 - 12)x - 8#
#x^3 + (-1)x^2 + (-10)x - 8#
#x^3 - 1x^2 - 10x - 8#
#x^3 - x^2 - 10x - 8#
