Respuesta :

84 chairs are Blue because 6×18-6×4=84
6 rows with 18 chairs each.

Total number of chairs = 6 * 18 =  108 chairs.


4 rows of 6 chairs are brown : 

Total = 4 * 6 = 24 chairs are brown.

Number of chairs that are blue =  Total - number of brown = 108 - 24 = 84

84 chairs are blue.

I hope this explains it.