Kelly is a salesperson at a shoe store, where she must sell a pre-set number of pairs of shoes each month. at the end of each workday, the number of pairs of shoes that she has left to sell that month is given by the equation s = 300 − 15x, where s is the number of pairs of shoes kelly still needs to sell and x is the number of days she has worked that month. what is the meaning of the number 300 in this equation?

a) kelly must sell 300 pairs of shoes per day.
b) kelly must sell 300 pairs of shoes per week.
c) kelly must sell 300 pairs of shoes each month.
d) kelly will sell the pairs of shoes in 300 days.