Answer
$-x^2-17xy-3y^2$; degree is $2$
Work Step by Step
Start by breaking down the parentheses. Then combine like terms to simplify. The degree is the power of the highest exponent.
$(7x^2-8xy+y^2)+(-8x^2-9xy-4y^2)$
$7x^2-8xy+y^2-8x^2-9xy-4y^2$
$-x^2-17xy-3y^2$
