Which function is represented in this graph

Can you guys plz answer this question in order and quickly plz i will give 30 points

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 work day 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 pair 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

If your teacher tells you to do questions 6 through 19 in your math book for homework, how many questions is that