Martha has 6/2=<<6/2=3>>3 yellow butterflies.

Martha has 6+3=<<6+3=9>>9 blue and yellow butterflies.

Martha has 19-9=<<19-9=10>>10 black butterflies.

# Answer

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<|im_start|>system
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<|im_start|>user
Martha has 19 butterflies in her collection. She has twice as many blue butterflies as yellow butterflies. The rest of her butterflies are black. If Martha has 6 blue butterflies, how many black butterflies does she have?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
10
Martha has 19 butterflies in her collection. She has twice as many blue butterflies as yellow butterflies. The rest of her butterflies are black. If Martha has 6 blue butterflies, how many black butterflies does she have?
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