Level 13 - figure out gas price


I was looking at this solution https://medium.com/coinmonks/ethernaut-lvl-13-gatekeeper-1-walkthrough-how-to-calculate-smart-contract-gas-consumption-and-eb4b042d3009
I was trying to figure out the gas price. As per the solution above it advises us to go on etherscan and check the contract specifiy however since the contract is not signed with do not have access to these informations like which compiler was used to compile as well as wether or not it was optimized.

Any help is appreciated.

Thank you

I found a way around using the https://rinkeby.etherscan.io/vmtrace?txhash=0x35473dd4c423d3eb9bd67c1977970747f912c15364835f7f2cf23838e0990d8e
but still I am confused. Once I found the "GAS" opcode. For example using the link above I see that the whole transaction cost 5758 in gas.
When I look for the GAS opcode I see that the value after is 262. I do the difference 5758 - 262 = 5496. I add 81910 to 5496 in order to make sure my transaction go through but still it is always reverting at the same time.
My AttackContract code is the following (the one from the solution):

contract AttackGateKeeper {
    Gate public gateKeeper = Gate(0x7CD437b6f550e603882Cd40275cf4B77B3132D64);
    bytes8 public byteKey = bytes8(tx.origin) & 0xFFFFFFFF0000FFFF;
    function callGate3() public {
        // bytes8 byteKey = convertBytes(msg.sender);
        gateKeeper.call.gas(87404)(bytes4(keccak256("enter(bytes8)")), byteKey);

I am sure what is having my transaction revert is this gas requirement. Anyone has any idea what I am doing wrong?
Thank you
What I am doing wrong above is that I am deducting from the all transaction cost which I souldnt. I should do it from after the call function is made but I am not sure from what optcode exactly.