A retailer purchased a delivery van for $21,000 on 1 July 2017. It was planned to keep the van until it had travelled 60,000 kilometres and then trade it in. The expected trade in value as $6,000.

The schedule of actual distance travelled was:

30 June 2018: 20,000 kms.

30 June 2019: 15,000 kms.

30 June 2020: 15,000 kms.

30 June 2021: 10,000 kms.

Using the units of production method the amount of depreciation charged for the year ended 30 June 2021 was $________. Record your answer in whole $ only.