I am currently revising over some past papers and this question has come up which I am having problems with. My notes don't show how to solve this and I don't have any worked examples. So far from looking on the internet, I have seen two methods. The first is using an equation for energy and the second is to use KVL for each coil and then substituting the equations. I've tried to understand using both of these methods but I still can't apply to this question. http://img714.imageshack.us/img714/3693/elecprob.jpg [Broken] Uploaded with ImageShack.us If anyone could give me pointers on what I need to be doing, or a brief example of how it's done, it would be greatly appreciated as I'm having a hard time getting my head around it. Thanks.