Final answer:
The total cost of the jet ski rental is $54.
Step-by-step explanation:
To find the total cost of the jet ski rental, we need to add the flat fee of $18 to the additional charge per hour. Since Todd rented the jet ski for 3 hours, we multiply the $12 charge per hour by 3. Then, we add the flat fee of $18 to get the total cost.
Therefore, the total cost of the rental is $18 + ($12 x 3) = $18 + $36 = $54.