To determine which orchard is cheaper, we need to calculate the total cost for each option given that there are 18 students.
For Orchard A:
- Admission cost is $9 per person.
- Number of people (students + chaperones) = 18 students + 3 chaperones = 21 people.
- Total cost at Orchard A = 21 people × $9/person = $189.
For Orchard B:
- Admission cost is $10 per person.
- Number of people (students + chaperones) = 18 students + 1 chaperone = 19 people.
- Total cost at Orchard B = 19 people × $10/person = $190.
Now we compare the total costs:
- Total cost for Orchard A: $189
- Total cost for Orchard B: $190
Therefore, Orchard A is cheaper for the class of 18 students.
The answer is: Orchard A.