(Caveat: I don't do AS2, so I might be getting some things wrong.)
Answer_txt.text == TextBox_txt + TextBox1_txt
That's your problem. TextBox_txt and TextBox1_txt are objects. Obviously, you want TextBox_txt.text and TextBox1_txt.text.
However, you've still got another problem after that. "+" in a string context is concatenation, not addition. In other words, 5 + 2 gives you 7, but "5" + "2" gives you "52". So you need to convert them to numbers before trying to add them. I'm not sure of the syntax to do that in AS2 off-hand.