How long will you have studied English when you will have finished this course?
Oh, at the end of this course I will have studied English for a total of twenty seven years.
Twenty seven years? But you still have not mastered the English language!
Ha, ha, ha. That shows how difficult English is to learn, and how determined I am to learn it!!
Besides, I know many people who will have spent more years studying English than I, and they do not even know the alphabet.