You'll notice that this address has received only 1 transaction.  The transaction ID where the bitcoins were received (where the output was created) was:
8dc0aa6a5022868490245fd4b10c47bccdaa0358cb24ed5ad3d09c99fac39f0e

If you look at that transaction you can see the outputs:

https://blockchain.info/rawtx/8dc0aa6a5022868490245fd4b10c47bccdaa0358cb24ed5ad3d09c99fac39f0e?format=json

Notice from that JSON output that there are two outputs ("out" array with two array elements).  The first output of the array is the one sent to "addr" 1g89wGhWxuQGGqGxVG6dZMzTTSVMWqWj6.  The index is indicated in the blockchain.info web interface in the array element with the "n" label.  So in this case, it is array element 0.

{
      "spent":false,
      "tx_index":114922761,
      "type":0,
      "addr":"1g89wGhWxuQGGqGxVG6dZMzTTSVMWqWj6",
      "value":4999000,
      "n":0,
      "script":"76a914076631c59ba595332917d7b6705006345233e46388ac"
},

How you determine this in your software will depend what interface you are using to access the data.  There are several services with their own API that you could use, or you could just use the Bitcoin Core interface.

If you are using Bitcoin Core, then you can use "listunspent" to get the list of all unspent outputs that the wallet has full control over.  You could also use "getrawtransaction" and/or "decoderawtransaction" to get information about specific transactions if you know the transactionID.


An unsigned transaction is not a valid transaction.  All nodes will reject it, and miners will not confirm it.  Therefore, you will need to use "signrawtransaction" before you can "sendrawtransaction"