10. Property and Equipment, Net

Property and equipment, net consisted of the following (in thousands):

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As of March 31, 2022 and December 31, 2021, the net book value of internal-use software was $1.7 million and $1.0 million, respectively. Depreciation expense and amortization expense related to property and equipment was $0.9 million and $0.5 million for the three months ended March 31, 2022 and 2021, respectively, which included amortization expense of internal-use software of less than $0.1 million and $0 for the three months ended March 31, 2022 and 2021, respectively.

Leased equipment and the related accumulated depreciation were as follows (in thousands):

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Depreciation related to leased units was $0.8 million and $0.4 million during the three months ended March 31, 2022 and 2021, respectively. Depreciable lives generally range from 4 to 7 years, consistent with the Company’s planned and historical usage of the equipment subject to operating leases.

Impairment of property and equipment was $0.1 million for the three months ended March 31, 2022. There was no impairment recognized for the three months ended March 31, 2021. This related to Edge units and Express prototype units that were removed from service and retired. The Company is transitioning its domestic customers from the Edge units to the most current Express units, which also resulted in an impairment of the remaining economic value of such assets.