Ok so first you will need 3 bags since 12*2 is 24 that wont be enough for the whole class so 12*3= 36 so now that we figured out how many bags we need now we have to multiply $8.00 by three the answer is $24
You have not given any graphs to choose from but x=-3 would be the graph that has a vertical line running through every point that has -3 as an x coordinate and would cross the x axis (the horizontal axis) at -3