What day is it?
If I said that in three days' time it would be a Thursday, I am sure that most of you would have no difficulty telling me that today was a Monday.
Try this one then. Three days ago, yesterday was the day before Sunday. What day will it be tomorrow?

Ans: Thursday.Think about it. Let today be X. Three days ago is X-3.  Yesterday on that day is X-4, which was the day before Sunday, which is Saturday. So today is 4 days after Saturday, which is Wednesday. So tomorrow will be Thursday.