Singapore Air Sets \$7.35 Bln Boeing Order  SINGAPORE/CHICAGO (Reuters) - Singapore Airlines Ltd.  &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=SIAL.SI target=/stocks/quickinfo/fullquote"&gt;SIAL.SI&lt;/A&gt; plans to buy up to 31 Boeing Co. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=BA.N target=/stocks/quickinfo/fullquote"&gt;BA.N&lt;/A&gt; long-range  777-300ER planes worth about \$7.35 billion, the carrier said on  Wednesday.