Answer
$-5x^4-4xy-9y^3$
Work Step by Step
Consider the given polynomial $(x^4-7xy-5y^3)-(6x^4-3xy+4y^3)$
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, $(x^4-7xy-5y^3)+(-6x^4+3xy-4y^3)=x^4-7xy-5y^3-6x^4+3xy-4y^3$
or, $=x^4-6x^4-7xy+3xy-5y^3-4y^3$
or, $=-5x^4-4xy-9y^3$
