#### Answer

$-1$

#### Work Step by Step

Step 1: $\frac{7-x}{x-7}$
Step 2: $\frac{7-x}{-(-x+7)}$
Step 3: $\frac{7-x}{-(7-x)}$
Step 4: Cancelling the expression (7-x) as it is common to both the numerator and denominator, the expression becomes $\frac{1}{-1}=-1$.