I don't think you can do this without additional information. This is what I'd start with:

There are a couple of variables here that we don't know; namely:

However, the question implies the following:

Which means:

Which we can plug in to the original equation:

But what about ? Well, let's explore the Bayesian equations for this. The first one that comes to mind is:

This might help, because, remember:

Which means that:

So let's plug those in:

And now let's rearrange it:

Now you should be able to plug that in and solve for