Final answer:
The domain for the function is 0 ≤ r ≤ 18, and the range is $0 ≤ an ≤ $31.5.
Step-by-step explanation:
The domain and range for the function an = 1.75r can be determined based on the given information.
Domain: In this case, domain represents the possible values for 'r', which is the number of rides Charlie goes on. Since Charlie can go on any number of rides from 0 to 18, the reasonable domain for this function is 0 ≤ r ≤ 18.
Range: The range represents the possible values for 'an', which is the total amount of money Charlie will spend. The cost of each ride is $1.75, so the range for this function is $0 ≤ an ≤ $31.5.