Thanks in advance
Without really answering the question it might help you to think about two things:
1) what is d, if d=0 then you have the same answer!
2) if it had to do with passing through the barrier shouldn't the depth u be of interest as well? in the sense that there is no passing through an infinite barrier, but if u is not quantatively involved then passing to the limit u goes to infinity will not end you up in the case of the infinite well.
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