Lets set up some variables:
1st envelope: 2nd envelope: 3rd envelope:Now let us set up some equations based of the facts:
Now we could try some numbers out since there isn't really any other way I could solve this so far...
but we do know that the sum of and must be even since they equal
After you tried it out for a little bit, when = 2, then = 8, and . These three values meet the criteria and we have our answer.
Hope that helped!