#### Answer

a) $1$
b) $-1$

#### Work Step by Step

a) We use the commutative property of addition to simplify the expression:
$\frac{x+4}{4+x} = \frac{x+4}{x+4} = 1$
b) Recognize that the numerator and denominator are opposites. That is, $x-4 = -1(4-x)$. Substituting this into the original fraction, we see:
$\frac{-1(4-x)}{4-x} = \frac{-1}{1} = -1$