to win the tickets for their next concert all you have to do

to win the tickets for their next concert 这是目的状语,all 是主语 ,you have to do 是all的定语从句,is是谓语,answer this question 是表语,不过你应该在answer前加to,因为is和to都是动词,用to隔开.为了赢得他们下一次的音乐会入场券,所有你要做的事就是去回答这个问题.back to 是返回到.的意思.是指演讲的内容更返回到音乐的话题上来.
I hope to help you!