Question 121294
If the larger number is n, then the smaller is n - 12.  {{{(n-12)+2n=39}}}


 {{{(n-12)+2n=39}}}


{{{3n-12=39}}}


{{{3n=39+12=51}}}


{{{n=17}}}


Check:  if the larger is 17, the smaller must be 17 - 12 = 5.  Twice the larger is 34 plus 5 is 39 -- checks.