Let's just say that the room is 8 meters long and 7 meters wide.
If Beibei's room is 4 meters wide, there are two situations. One is that Beibei's room is 4 meters wide and 7 meters long, so Beibei's room area is 28 square meters. Secondly, Beibei's room is 4 meters wide and 8 meters long, so Beibei's room area is 32 square meters.
Even if the length and width of the room are not hypothetical, it can be done by the above method, that is, if the big room is rectangular, there are two possibilities for Beibei's room area, one is four times the length of the room and the other is four times the width of the room.
I hope it helps you.