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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _calculate_areas(self, label):
 """Calculate areas for multiple labels"""

        heights = np.maximum(0, label[:, 3] - label[:, 1])
        widths = np.maximum(0, label[:, 2] - label[:, 0])
        return heights * widths