Rao Corporation has the following balance sheet.

Cash	$ 10		Accounts payable	$ 20
Short-term investments			Accruals	20
Accounts receivable	50		Notes payable	50
Inventory	40		Current liabilities	$ 90
Current assets	$130		Long-term debt	0
Net fixed assets	100		Common equity	30
			Retained earnings	50
Total assets	$230		Total liab. & equity	$230

How much net operating working capital does the firm have?