trigonometry
posted by Cindy .
Find the number of cans stacked in a display if there are 30 rows of cans with six on the top row, ten on the second row, 14 on the third row and so on.
I know it's the sum of an arithmetic sequence, but I'm not sure exactly what to do.

The highest row has 6 cans
The lowest row (29 rows down from the top) has 6 + (29*4) = 122 cans
The average number in a row is (122+6)/2 = 64 cans.
The total number of cans is 30x64 = 192