$3\times (2a+4)=3(2a+4)=6a+12$ 
If a number is written as $2a+4$, then $3$ times the number is~\uline{~~~~~~~~~~}~. (adapted from 1977 Math League.com contest problem, 8\textsuperscript{th}~Grade, Question \#31) 
Options:
  $6a+4$ 
  $2a+7$ 
  $6a+12$ 
  $32a+34$ 