Establish the condition required to make the current through ZE in fig

[brazier84]

 

[NascentOxygen]

Welcome to Physics Forums, brazier84. The way these forums work is that you show your attempt at the solution, and someone will then try to give you some pointers on how to proceed, or discuss where you may have gone wrong. It goes without saying that those who fail to follow this basic requirement cannot expect to receive any help.

I notice there is not even a complete question specification in your post.

This is not a good start...

 

[brazier84]

Apologies comments taken on board. I wrote or thought I wrote out the question in full. I will make an attempt at the answer and post that