MATH
posted by Katie .
a pile of bricks has 85 bricks in the bottom row, 79 bricks in the second row, 73 in the third row, and so on until there is only 1 brick in the top row.
how many bricks are in the 12th row?
how many rows are there in all?

You have an arithmetic sequence where
a = 85 , d = 6
12th row = 85 + 11(6) = 19
row(n ) = a + (n1)d
1 = 85 + (n1)(6)
1 = 85  6n + 6
6n = 90
n = 15
there are 15 rows