Jessica is selling books during the summer to earn money for college. She earns a commission on each sale but has to pay for her own expenses. After a month of driving from neighborhood to neighborhood and walking door-to-door, she figures out that her weekly earnings are approximately a linear function of the number of doors she knocks on.

She writes the equation of the function like this: E(x)=10x-30, where x is the number of doors she knocks on during the week and E open argument x close argument is her earnings for the week in dollars.

What of the following are reasonable interpretations of the y-intercept of Jessica's function?