Your question is a little difficult. The structure is weird if you don't giving more information about why you would like to use it. --------------------Sorry, my google chrome crashed.

Your question is a little difficult. The structure is weird if you don't giving more information about why you would like to use it.

可不是嘛shows your consent.=tell me about it! "这不"is to draw people's attention.=look! 他这会正在办.... 伤脑筋呢 He is doing sth which is nerve-wracking to him.

他在家里呆了一天？ 可不是嘛！这不，他这会儿又在为办手续的事情伤脑筋呢。 “可不是嘛”，就是肯定对方说的话。“这不”就像“你看”，正在发生的事。