If $$20$$ years ago Allen was half as old as he is today, then today he is $$40$$. Thus, $$10$$ years ago he was $$30$$. 
If $$20$$ years ago Allen was half as old as he is today, how old was he $$10$$ years ago? 
Options:
* $$20$$ 
* $$30$$ 
* $$40$$ 
* $$50$$ 