@Charles: I know we all make mistakes. Have you actual read their lengthy explanation on why their wrong answer is correct? After they already read so many people telling them the right answer already? And I really do not see how one can forgot or confused about it, because with my terrible memory, who I still cannot remember my parents bday except my bro's 123, I find it very easy to remember. Actually you only need to remember one thing only, +- has () around it. And that's it. Everything else really has no brainer, like tiny power number attached to a large number, which is very obvious the tiny number belongs to the attaching number.