没有人回答吗？

I think the answer should be an expectation. X(t) is a random number since first passage time is random.

How can I do it ?

I just the give the general step which may not work for your case. But anyway, it is hint.

Well the first step is of course solve this SDE. I assume you can do that.

You then get X(t) expressed in time t and B(t). So what you need to find is just the time when B(t) first come to -3. Let's say that time=tao.

The first passage time' expectation should be included in the text book. E(tao|B(tao)=-3), so put tao and B(tao)=-3 into X(t), you get the result.

I can't give you the detailed solution since that is not good for you.

Thanks a lot for answering my so many questions .You are a very good boy.