Why the interviewer is asking this question: The interviewer is asking to align expectations for the role with your long-term expectations. While interviewers typically want solid alignment on near term (i.e. under 5 years) expectations, more latitude can and will be given for longer term goals.
If they don't want to give benefits to stocker and cashiers they should have part time hours and paid $17.50 per hour no benefits. Also how many teenagers would like a parttime job from 3 pm until 7pm and maybe get the pay they give their cashiers $8 -9 an hour.
Look at the first scatterplot again. As the number of hours worked per week moves past 50 or 60, drivers start to reliably earn somewhere between $20 and $35 an hour. But for those working part time, and especially less than 30 hours, it's a crapshoot. Some are averaging $25 net per hour.