考题90题第84题答案是5 variables, 30 observations。可是我系统里跑出来的结果是4个variables, 30 observation

data work.roth_ira;
do year=1 to 30;
savings + 5000;
do month=1 to 12;
   int=savings * (.05/12);
   savings + int;
   end;
   output;
   end;
   run;

求解答