# `BalancerLiquidity.join` exercise Write your code inside the [`BalancerLiquidity` contract](https://github.com/Cyfrin/defi-reth/blob/main/foundry/src/exercises/BalancerLiquidity.sol) This exercise is design for you to gain experience adding liquidity to Balancer. ```solidity function join(uint256 rethAmount, uint256 wethAmount) external { // Write your code here } ``` ## Instructions 1. **Transfer rETH and WETH from msg.sender** - Transfer rETH and WETH from `msg.sender` - Approve Balancer (`address(vault)`) to spend these tokens 2. **Add liquidity** - Call internal function `_join` to add liquidity. - Prepare parameters `assets` and `maxAmountsIn`. Token addresses and max amounts in must be ordered as rETH and then WETH. - Set the recipient of LP token (BPT) to `msg.sender`. 3. **Refund** - Send any left over rETH and WETH in this contract to `msg.sender`. ## Testing ```shell forge test --fork-url $FORK_URL --match-path test/exercise-balancer.sol --match-test test_join -vvv ```