At the local grocery store, cans of beans are arranged in rows. the number of cans in each row forms an arithmetic sequence. there are 85 cans in row 1, 78 cans in row 2, 71 cans in row 3, and so on. one row contains 29 cans. which row is this?

As you can tell, they are subtracting 7 cans each row. You could make a table which would be kind of like this with an ordered pair.
1,85
2,78
3,71
and on
Or you can find what 85-29 equals. Once you find 56, you divide it by 7. That gives you 8 but you have to take in consideration that row one has 85 and that is when it started decreasing, so you have to add a 1 to the 8. This allows you to know that it is row 9 that contains 29 cans. You can even finish your table to make sure.
4,64
5,57
6,50
7,43
8,36
9,29

I hope this helps!!