Can someone please help me with math

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

Rectangle pqrs has length a and width 4b. the x-axis bisects ps and qr what are the coordinates of the vertices

Christina can paint 420 square feet in 105 minutes. which unit rate describes the scenario?