First, we need to determine how much you were exceeding the speed limit. The speed limit is 55 mph, and you were driving at 73 mph. To find out how much over the limit you were driving, we subtract the speed limit from your speed:
[tex]\[ 73 \, \text{mph} - 55 \, \text{mph} = 18 \, \text{mph} \][/tex]
So, you were driving 18 mph over the speed limit.
Next, we need to determine the fine based on the amount by which you exceeded the speed limit. Here are the fine brackets:
1. If you exceed the speed limit by 10 mph or less, the fine is [tex]$106.
2. If you exceed the speed limit by more than 10 mph but not more than 20 mph, the fine is $[/tex]146.
3. If you exceed the speed limit by more than 20 mph but not more than 30 mph, the fine is [tex]$186.
4. If you exceed the speed limit by more than 30 mph, the fine is $[/tex]206.
Since you exceeded the speed limit by 18 mph, you fall into the second bracket (more than 10 mph but not more than 20 mph).
Therefore, the fine for driving 18 mph over the speed limit is:
[tex]\[ \boxed{146} \][/tex]
So, the correct answer is:
b. $146
