How I do I calculate the refund amount from the decoded createRetryableTicket function parmas and tx information?

For example, this is the retryable creation transaction:
https://arbiscan.io/tx/0xcb9d02346c1063ce0d13f2a2c56ae834c5466e91f29fddd4a8c57055ab2aaf8a
Note 0.00016638939737323 deposited and 0.00000032912933 tx fee(submission fee)

This is the auto redeem tx
https://arbiscan.io/tx/0x6cbe6a7a1715c263df05dc7165ff73febf93c100fea04a2ef69896fd75c14783
Note 0.00007917939407 tx fee0.00016638939737323 - 0.00000032912933 - 0.00007917939407 = 0.00008688087 refund
 
In general, these transactions will be in the same block of the l2 tx, but he can use this script https://github.com/OffchainLabs/arbitrum-sdk/blob/master/scripts/checkRetryableStatus.ts to locate them