Given:
Working capital = 180,000
debt-to-asset ratio = 40%

Working capital = Current assets – current liabilities
debt-to-asset ratio = total liabilities / total assets

I found a similar problem but it has an accompanying balance sheet.
Total current liabilities =    75,000
Total long term assets = 420,000

Current Assets = Working capital + current liabilities
Current assets = 180,000 + 75,000
Current assets = 255,000

Total Assets = Current Assets + Long term Assets
Total Assets = 255,000 + 420,000
Total Assets = 675,000

debt-to-assets ratio = total liabilities / total assets
40% = total liabilities / 675,000
total liabilities = 675,000 x 40%
total liabilities =  270,000

Asset = Liabilities + Equity
Equity = Assets – Liabilities
Equity = 675,000 – 270,000
Equity = 405,000