## Elementary Algebra

$5$
Combining like terms, the given expression simplifies to: $5x-7y-8x+3y$ =$5x-8x+3y-7y$ =$x(5-8)+y(3-7)$ =$-3x-4y$ We then substitute $x=9$ and $y=-8$ in the expression and simplify: $-3x-4y$ =$-3(9)-4(-8)$ =$-27+32$ =$5$