$$7y+1-x-1=7y-x$$ 
Mike has $7y+1$ cans of coke. He gives his friends $$x$$ cans of coke. And he takes one out. How many cans of coke does he have left? 
Options:
[1] $$7y + 1$$ 
[2] $$7y + 1 -x$$ 
[3] $$7y-x$$ 
[4] $$7y$$ 