Sealed Solution Musab

How I tried solving this problem was that I found all the pairs of numbers that add up to 8.They are 0 and 8,1 and 7,2 and 6 and 3 and 5.I started off with 0 and 8 and I used the rest of the numbers which were 1,2,3,4,5,6,7 and 9 to see if I could make up all the envelopes by adding 2 numbers from those digits without using a number more than once.I repeated that process by using all the possible combinations of the numbers that add up to 8 and used the remaining numbers to make all the envelopes.