Sentence:  In America alone, people spent $170 <WSD>billion</WSD> on “direct marketing”—junk mail of both the physical and electronic varieties—last year. Yet of those who received unsolicited adverts through the post, only 3% bought anything as a result. 
Meaning of the word marked with <WSD> tags:  a thousand million: 1 followed by nine zeros, 109; a milliard