A 7-month-old female presents to the emergency department after several hours of listlessness and occasional vomiting. Her last bowel movement was two hours earlier, and was noted to be non-bloody by the mother. Upon physical examination, she was noted to be afebrile, with a soft, non-tender, non-distended abdomen with no palpable masses. An abdominal ultrasound was ordered and read as equivocal. An upright abdominal radiograph is ordered after the ultrasound and demonstrated an absence of bowel gas in the left upper quadrant.
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What is the Tx?