On december 31, 2015, a company had assets of $16 billion and stockholders' equity of $8 billion. that same company had assets of $20 billion and stockholders' equity of $9 billion as of december 31, 2016. during 2016, the company reported total sales revenue of $9 billion and total expenses of $7 billion. what is the company's debt-to-assets ratio on december 31, 2016?