Two endpoints and all points in between them

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

The midpoints of the sides of the large square are joined to form a smaller square. what is the area of the smaller square

Which equation is y = -6x2 + 3x + 2 rewritten in vertex form?