What is the amount of depreciation? And what is lagged fixed asset?

Assumptions 2021 Units Sold 3,500 Sale price (unit price) 100.00$ Cost of Goods Sold Variable costs (per unit sold) 60$ SG&A Fixed cost 12,000$ Variable costs (% of revenue) 10% Depreciation (% of lagged fixed assets) 15% Interest Expense (% of lagged NP and LTD) 10% Relevant Tax Rate 20% Days Sales in Inventory 45 Days Sales in Receivables 40 Days Payables Outstanding 35