June made a design with 20 equal tiles. Three tiles are yellow and the number of blue tiles is one more than the number of yellow tiles. Six tiles are purple and the remaining tiles are white.  How many white tiles are there?
There are 3 + 1 = <<3+1=4>>4 blue tiles.
There are a total of 3 + 4 + 6 = <<3+4+6=13>>13 tiles are yellow, blue, and purple.
Hence, 20 - 13 = <<20-13=7>>7 tiles are white.
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