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) = 20x - 50, where x is the number of doors she knocks on during the week and e(x) is her earnings for the week in dollars.

what does the slope of jessica's function represent?

a. for each additional set of books she sells, her earnings will increase by $20.

b. for each additional door she knocks on, her earnings will increase by $20.

c. for each additional set of books she sells, her earnings will increase by $50.

d. for each additional door she knocks on, her earnings will increase by $50.