I wish I could type in Mandarin or Cantanese so you could understand, Mr. Cho. But I'll give it one more try and then you're on your own.
Yes, we're talking about people getting minimum wage in Seattle in 2015/16. But, that isn't $13/hr like you wrongly implied, at least not for most people. We are talking about the difference between the minimum wage pre-2015 and the average minimum wage paid by those businesses required to raise their wages.
Even though the article doesn't tell us what that average is, we can ascertain that the number is somewhere between $11 and $13, but it's certainly not $13. So, pick any value and plug it in. Hopefully then you'll get the fact that socialized wage increases leads to lower hours.