Answer
$2x^4y^2+11x^3y-y-8x$, degree 6.
Work Step by Step
$$(5x^4y^2+6x^3y-7y)-(3x^4y^2-5x^3y-6y+8x)$$ $$=(5x^4y^2-3x^4y^2)+[6x^3y-(-5x^3y)]+[-7y-(-6y)]-8x$$ $$=2x^4y^2+(6x^3y+5x^3y)+(-7y+6y)-8x$$ $$=2x^4y^2+11x^3y-y-8x$$
This is degree 6. To find the degree of a term, add together the exponents of all the variables in a term (4+2=6). The term with the largest degree determines the degree of the expression.
