Friend experienced this problem

But there is only 1 box
Where the * do I fill the 2nd answer?

I don't know, maybe you should "use a comma to separate answers as needed".

No, it means OP is wrong, since the answer is '11/2 , -11/2'.
There are posts like these which show a correct answer marked wrong, this is a case of a WRONG answer, marked WRONG, with an explanation as to why you are wrong. Your ineptitude at maths does not make the programm shitty.