The manager of a store is stacking boxes for a display. there are 18 boxes on the bottom row. each successive row has one less box than the previous row. the expression mc015-1.jpg represents the total number of boxes in the display for the first 15 rows. how many boxes are in the display? 18 22 165 330

So you start with 23
for every row up you have -3
equation is
# of boxes= 23- 3x
x representing the number of rows above the bottom
# of boxes= 23- 3x=
23-3(5)= 8 
5 for the top row
bottom row has 23
1 row above 23-3(x)=20
2 row above 23-3(x)= 17
323-3(x)= 14
423-3(x)=11
5...23-3(x)= 8
therefore just add all boxes each row has
23+20+17+14+11+8= 83 
I hope this helps