First I started by doing 7 first as it was the first number in the order of envelopes but quickly realised this was not helpful and that i needed to do it in a size specific order. After deciding to do it in descending order instead of ascending I started writing out all the possible number pairs that could make the number on the front of the envelope, I found 9+5 and 8+6 for 14, 7+6, 4+9 and 8+5 for 13, 0+8, 5+3, 1+7 and 6+2 for 8, 3+4, 0+7, 2+5 and 6+1 for 7 and 2+1 and 0+3 for 3. I continued to rotate between each of these pairs for each number on the envelope until I found a correct solution. To make this process quicker I often looked ahead and at what the outcome was of using different pairs in the long run, after finding all 3 solutions I simply checked that there weren’t any more by using all the numbers in different sequences and checking that the numbers would not be used twice in the further steps of finding the sequences. After double checking my addition I knew I had the right answer to the questions and had figured out all possible sequences, my answers were:
14 13 8 7 3
9+5 7+6 0+8 3+4 2+1
8+6 4+9 5+3 0+7 2+1
8+6 4+9 1+7 2+5 0+3