On December 31, 2018, a company had assets of $35 billion and stockholders' equity of $30 billion. That same company had assets of $49 billion and stockholders' equity of $11 billion as of December 31, 2019. During 2019, the company reported total sales revenue of $28 billion and total expenses of $26 billion. What is the company's debt-to-assets ratio on December 31, 2019?