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) = 7x - 25, 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? ( as soon as possible) a. for each additional set of books she sells, her earnings will increase by $7. b. for each additional door she knocks on, her earnings will increase by $7. c. for each additional set of books she sells, her earnings will increase by $25. d. for each additional door she knocks on, her earnings will increase by $25.