Answer
$a)$ $f(x+h)=-2x-2h+5$
$b)$ $f(x+h)-f(x)=-2h$
$c)$ $\frac{f(x+h)-f(x)}{h}=-2$
Work Step by Step
$a)$
$$f(x)=-2x+5$$
Replace $x$ with $x+h$:
$$f(x+h)=-2(x+h)+5$$
$$f(x+h)=-2x-2h+5$$
$b)$
$$f(x+h)-f(x)$$
Substitute corresponding expressions:
$$-2x-2h+5-(-2x+5)$$
$$-2x-2h+5+2x-5=-2h$$
$c)$
$$\frac{f(x+h)-f(x)}{h}$$
Substitute corresponding expression for numerator:
$$\frac{-2h}{h}=-2$$
