First figure out how many total flowers Martha is going to buy by dividing her total spending by the price per flower: $2700 / $15/flower = <<2700/15=180>>180 flowers
Now figure out how many flowers are in each centerpiece by dividing the total number of flowers by the number of centerpieces: 180 flowers / 6 centerpieces = <<180/6=30>>30 flowers / centerpiece
Now figure out how many orchids are in each centerpiece by multiplying the number of roses per centerpiece by 2: 8 roses/centerpiece * 2 = <<8*2=16>>16 orchids/centerpiece
Now subtract the number of roses and orchids per centerpiece from the total number of flowers per centerpiece to find the number of lilies per centerpiece: 30 flowers - 16 orchids - 8 roses = <<30-16-8=6>>6 lilies
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