Answer:
Option A is correct that is $18
Step-by-step explanation:
We have been given an information that is
c=$54 when n =9
when 9 gives 54
Then 1 gives 54/9
cost for one sandwich that is when n=1 then 
We need to find the cost for 3 sandwiches that is when n =3 then
when cost for one sandwich is 54/9 then cost for 3 sandwiches is 
Therefore, Option A is correct tha is $18.