Nancy can hula hoop for 10 minutes.  Casey can hula hoop 3 minutes less than Nancy.  Morgan can hula hoop three times as long as Casey.  How long can Morgan hula hoop? Let's think step by step and output the final answer after "####".
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Casey can hula hoop 3 minutes less than Nancy so she can hula hoop for 10-3 = <<10-3=7>>7 minutes
Morgan can hula hoop three times as long as Casey, who can hula hoop for 7 minutes, so she can hula hoop for 3*7 = <<3*7=21>>21 minutes
#### 21
Nancy can hula hoop for 10 minutes.  Casey can hula hoop 3 minutes less than Nancy.  Morgan can hula hoop three times as long as Casey.  How long can Morgan hula hoop?
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