The answer from summing up x^4 - 3x +1, 4x^2 - 2x +8 and x^3 - 9 would be x^4 + x³ + 4x² - 5x. This is adding first the highest power, in this case the highest is 4th power, do we need to add all the variable that is in 4th power then it will be followed by the next lower power.