12. A local boutique sells water bottles for a set price, plus an additional fee for each letter that customers would like engraved on their water bottle. The pricing for up to 4 engraved letters is
shown in the table below.
# of Letters
0
2
3
4
Total Cost
18.99
19.34
19.69
20.04
20.39
Write an equation to represent the relationship between the number of letters and the total cost.