我几个点不清楚1.Mega backdoor contribution 这部分对于50岁以下最大部分是66000-employee contribution-employer contribution,那这部分钱是存在什么账户里面?2. backdoor对于,The 2024 Roth IRA income limit for married couples filing jointly who want to contribute to a backdoor Roth IRA is between $230,000 and $240,000.那么对于超过这个数字的夫妻收入的家庭,那不就是不能放Roth IRA了吗?3.视频10‘28‘’为什么是从个人账户最多转账6600刀而不是6500刀?