First find the total number of blue-eyed kittens: 3 kittens + 4 kittens = <<3+4=7>>7 kittens
Then find the total number of brown-eyed kittens: 7 kittens + 6 kittens = <<7+6=13>>13 kittens
Then add the number of each type of kitten to find the total number of kittens: 7 kittens + 13 kittens = <<7+13=20>>20 kittens
Then divide the number of blue-eyed kittens by the total number of kittens and multiply by 100% to express the answer as a percentage: 7 kittens / 20 kittens * 100% = 35%
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