Answer
$f(a) =5 - 2a $
$f(a+h)= 5 - 2a - 2h$
$\frac{f(a+h) - f(a)}{h} =-2 $
Work Step by Step
$$f(x) = 5 - 2x$$
$f(a) = 5 - 2a $
$f(a+h)= 5 - 2(a +h) = 5 - 2a - 2h $
$\frac{f(a+h) - f(a)}{h} = \frac{(5 - 2a -2h) -(5-2a)}{h} $... simplify numerator
$=\frac {5-2a-2h-5+2a}{h}=\frac {-2h}{h}= -2 $