# `FlashLev.open` exercise Write your code inside the [`FlashLev` contract](https://github.com/Cyfrin/defi-reth/blob/main/foundry/src/exercises/FlashLev.sol). This exercise is designed to test your understanding of how to structure a smart contract function for initializing a leveraged position using a flash loan. ```solidity function open(OpenParams calldata params) external { // Write your code here } ``` ## Instructions 1. **Transfer collateral from `msg.sender`** - Transfer collateral from `msg.sender` into this contract. > **Hint:** Look into the struct `OpenParams` to find out how much collateral to pull in. 2. **Initiate a flash loan** - Encode flash loan data into `FlashLoanData`. - Call `flashLoan` to initiate a flash loan. > **Hint:** Look inside `AaveHelper` to see how to call the function `flashLoan`. 3. **Check health factor** - Require that the health factor after the position is created is greater than or equal the minimum health factor specified in the input `OpenParams.minHealthFactor`. > **Hint:** Look inside `AaveHelper` to see how to get the health factor. # `_flashLoanCallback` ```solidity function _flashLoanCallback( address token, uint256 amount, uint256 fee, bytes memory params ) internal override { // Write your code here } ``` ## Instructions 1. **Implement logic for opening a position** - Implement flash loan callback logic for opening a position. > **Hint:** > > - Look into `AaveHelper` for how to supply collateral and borrow stablecoin. > - Look into `SwapHelper` for how to swap tokens. 2. **Repay flash loan** - Approve Aave to repay flash loan amount. > **Hint:** > > - Address to approve is `pool`, initialized inside `AaveHelper`. > - Amount to approve for repayment is amount borrowed + fee.