其它
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) 
Overseas Competition->Knowledge Point->Calculation Modules->Basic Concepts of Equation->Equivalent Substitution->Using a Letter to Represent an Unknown Number
$3\times (2a+4)=3(2a+4)=6a+12$ 