There are 6 rows with 18 chairs in each row. in the center of the chairs, 4 rows of 6 chairs are brown. the rest of the chairs are blue. how many chairs are blue?

Multiply 6 times 18 and you get 108 chairs total. Subtract 6 by 4 and you get 2 rows left for blue. Multiply 4 by 6 and you get 24 in brown chairs all together. Then subtract 108 by 24 and you get 84 chairs all together for blue. So that means 2 rows with 42 blue chairs in each row.

The amount used= 13.04- 1.9 = 11.14