In response to complaints about high prices, a grocery chain runs the following advertising campaign: "If you pay your child $6 to go buy $50 worth of groceries, then your child makes twice as much on the trip as we do." You've collected the following information from the grocery chain's financial statements:

(millions)

 Sales $ 646  

 Net income 33  

 Total assets 497  

 Total debt 341  

What is the profit margin for the store? (in %)

(round to 4 decimal places)