data over175;
   set ia.dfwlax;
   length City $ 11;
   Total=sum(FirstClass,Economy);
   if Total le 175 then delete;
   if upcase(Dest)='DFW' then
      Revenue=sum(1500*FirstClass,900*Economy);
      City='Dallas';
   else if upcase(Dest)='LAX' then
      Revenue=sum(2000*FirstClass,1200*Economy);
      City='Los Angeles';
run;

日志：显示没有匹配的if-then子句，请问错误在哪里？

谢谢！