#### Answer

$C(x)=0.75x+2$

#### Work Step by Step

In a cost function of the form $C(x)=mx+b$,
m represents the marginal cost and
b represents the fixed cost.
Here,
b= $\$ 2$ (fixed cost) and
m= $\$ 0.75$ (the cost of parking a car for one half-hour).
Let
$x=$ the number of half-hours;
$C(x)=$ the cost of parking a car for $x$ half-hours.
$C(x)=0.75x+2$