Gilbert Company bought equipment several years ago and used the straight-line method to record depreciation expense. At the end of 2012, the adjusted trial balance shows the following balances related to this equipment: PP&E $100,000; Accumulated Depreciation $20,000; Depreciation Expense $5,000. How many years has the equipment been used?

A) 3 years

B) 4 years

C) 5 years

D) 40 years