Transaction hash calculation

Question

Calculating transaction hash incorrectly.

I need to calculate transaction hash.

I have:

1. SHA256(x)
2. Network Passphrase: "Public Global Stellar Network ; September 2015"
3. Future transaction XDR envelope (e.g.): "AAAAAgAAAAD3tky1miraP23z0mbKFWoE2t3hMmAfV/KN717oJCbQuAAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAABAAAAAPe2TLWaKto/bfPSZsoVagTa3eEyYB9X8o3vXugkJtC4AAAAAQAAAAD3tky1miraP23z0mbKFWoE2t3hMmAfV/KN717oJCbQuAAAAAAAAAAABfXhAAAAAAAAAAAA"

in the Stellar Laboratory, the hash is = "7022ff2300f5b51dfa21f5dfe08bb0315e4fd6a404844849ebd4239fe171659a"

Question. What binary data should go into the hash function?

Hash Transaction = SHA256(x). x = ?, SHA256("Public Glo..." + "AAAAAg...") ?