help around flashSwap

[fbabovic23]

Hey everyone,

I need help for understanding the last two lines in exercise in flashSwap of uniswap v2(https://github.com/Cyfrin/advanced-defi-2024/blob/main/foundry/test/uniswap-v2/solutions/UniswapV2FlashSwap.sol):

    function uniswapV2Call(
        address sender,
        uint256 amount0,
        uint256 amount1,
        bytes calldata data
    ) external {
        // Write your code here
        // Don’t change any other code

        // 1. Require msg.sender is pair contract
        // 2. Require sender is this contract
        // Alice -> FlashSwap ---- to = FlashSwap ----> UniswapV2Pair
        //                    <-- sender = FlashSwap --
        // Eve ------------ to = FlashSwap -----------> UniswapV2Pair
        //          FlashSwap <-- sender = Eve --------
        if (msg.sender != address(pair)) {
            revert NotPair();
        }
        // 2. Check sender is this contract
        if (sender != address(this)) {
            revert NotSender();
        }
        // 3. Decode token and caller from data
        (address token, address caller) = abi.decode(data, (address, address));
        // 4. Determine amount borrowed (only one of them is > 0)
        uint256 amount = token == token0 ? amount0 : amount1;

        // 5. Calculate flash swap fee and amount to repay
        // fee = borrowed amount * 3 / 997 + 1 to round up
        uint256 fee = ((amount * 3) / 997) + 1;
        uint256 amountToRepay = amount + fee;

        // 6. Get flash swap fee from caller
        IERC20(token).transferFrom(caller, address(this), fee);
        // 7. Repay Uniswap V2 pair
        IERC20(token).transfer(address(pair), amountToRepay);
    }
}

Why do we have to transfer fee amount to the this contract:
// 6. Get flash swap fee from caller IERC20(token).transferFrom(caller, address(this), fee);

when the fee is included in repaying to pair contract the amount that we borrowed + fee in this last line:
IERC20(token).transfer(address(pair), amountToRepay);

[EngrPips]

Why do we have to transfer fee amount to the this contract: // 6. Get flash swap fee from caller IERC20(token).transferFrom(caller, address(this), fee);

We have to transfer the fee from caller because they are the one that processed the flash swap and they are responsible for any fee attached to the swap fee process.

when the fee is included in repaying to pair contract the amount that we borrowed + fee in this last line:
IERC20(token).transfer(address(pair), amountToRepay);

I don't understand this question