Cancel common polynomial and integer factors. and fill in the blanks.
$\frac{x^2+6 x + 8}{x^2+7 x + 10} = ( x +$ $)$ $/ (x +$ $)$
For this identity to hold, $x$ must not equal .
Hint: If you have difficulties seeing how to factor the numerator and denominator set them to zero, solve the resulting equation, and deduce the appropriate linear factors from the solution. Then cancel the common factor in numerator and denominator.