I would think this is many solutions, the reason is because, there is no specific answer (y) so, x could be anything because it would have to equal to y, which could also be anything! I hope im right! Sorry if im wrong!
Since it starts with 2 envelopes, subtract 2 from 17 to get how many and in all 3 packs.
17 - 2 = 15
Now, we divide that number by 3 to get how many are in each envelope.
15 / 3 = 5
There are 5 envelopes in each pack.
This is simple, what is the total degree of a triangle? 180
so add up 70 + 30 is 100, the answer to x is 80