Half the gnomes have big noses, so 28 / 2 = <<28/2=14>>14 have big noses.
Three-quarters of the gnomes have red hats, so 28 * 3 / 4 = <<28*3/4=21>>21 gnomes have red hats.
There are 6 gnomes with blue hats and big noses, so there are 14 - 6 = 8 with red hats and big noses.
Thus, there are 21 - 8 = <<21-8=13>>13 gnomes with red hats that have small noses.
#### 13