Final answer:
The question asks for an estimate of total trips made by families but lacks crucial details such as trip frequency to provide an accurate answer.
Step-by-step explanation:
The question is requesting an estimate for the total number of trips made by 225 single-occupancy vehicle families in a given zone. To estimate the total number of trips, more specific information is needed such as the average number of trips made by a family per day or week. Without this information, it is not possible to provide an accurate estimate. The financial context provided, which mentions the low annual incomes of families and their ability to cover expenses, does not directly relate to trip estimation.