To find out how many hours Christiana should work, we need to subtract the $18 tip from the amount she needs to pay her car insurance ($130). This will give us the amount of money she still needs to earn without the tip.
$130 - $18 = $112
Now, we have the remaining amount that Christiana needs to earn, which is $112. Since Christiana earns $14 per hour, we can divide the remaining amount by her hourly wage to find out how many hours she should work.
$112 / $14 = 8
So, Christiana should work 8 additional hours to make enough money to pay her car insurance.