Answer: 
Step-by-step explanation:
I did this question a few months back, and I got this answer correct.
Here is your answer

Since the door will be in shape of a rectangle where,
length= 80 inches
breadth= 72 inches
So,
widht of largest mattress that can fit diagonally is diagonal of the door.
i.e.





HOPE IT IS USEFUL
Answer:
It's (D)
Step-by-step explanation:
Answer: it’s very good imo