Answer
$9x^3+4x^2-2x+1$
Work Step by Step
Consider the given polynomial
$(18x^3-2x^2-7x+8)-(9x^3-6x^2-5x+7)$
Need to drop the parentheses and will have to change the sign of each term of the second polynomial because of the presence of the negative outside.
Thus,
$(18x^3-2x^2-7x+8)-(9x^3-6x^2-5x+7)=18x^3-2x^2-7x+8-9x^3+6x^2+5x-7$
or, $=18x^3-9x^3-2x^2+6x^2-7x+5x+8-7$
or, $=9x^3+4x^2-2x+1$
