Corrine earns an hourly wage on top of her weekly gas allowance for her delivery job.
Her weekly earnings can be expressed as:
Earnings = 40 + 7.50h
When h=0, her earnings will be 40
This constant represents, the fixed gas allowance she is receiving for her delivery job. 7.50h represents that she get paid $7.50 for an hour of work.
So, the constant term in the expression represent her weekly gas allowance.