For finding the solution, you want to sum the revenue from each class of paying customers. There were 92-40 who were over 12 years and paid $48, so the revenue from those folks is (92-40)ยท48. This term is found in the first and last selections only.
There were 40-x customers who were in the age range 3โ12 years, so paid $36 each. The revenue from them is (40-x)ยท36. This term is found in the last selection only.
The appropriate choice is ...
... D.) (40 - x)ยท36 +(92 - 40)ยท48 = C