What Added to What Equals Two?

In the fourth round, 007 rolled a one.

Gu Mian and Liu Ruyan moved just one space before stopping. But this time, the room was finally no longer empty. It seemed the dungeon's "emergency repair" had worked pretty well.

Gu Mian had encountered the first ghost since entering the dungeon.

[Arithmetic Grid]

[What does 1 + 1 equal? The floor of the room has been evenly divided into sixteen squares, each containing a number chosen at random from one to nine. The pieces remaining in the room must memorize all sixteen numbers within thirty seconds. After thirty seconds, the numbers will disappear. There is a ghost in the room who likes doing math problems. Next, it will give you a number. The pieces must choose two blank squares whose original numbers add up to the number given by the ghost.]

[After the ghost asks its question, you must answer within one minute. Correctly write an equation to receive a reward. Failure will cost you a life.]

There was a countdown above this room, too. The thirty-second timer had already started.

All the rooms on the board were square. Black lines divided this room's floor into sixteen squares, each marked with a number.

The two squares beside Gu Mian's right foot were both marked with ones.

But he didn't continue looking at the numbers in the squares. Instead, he turned to search for the ghost.

It took him a while to find it. The ghost was cowering in a corner, trembling so badly that it was easy to miss if you weren't looking closely.

Gu Mian stepped over the two ones on the floor and walked over. He grabbed the trembling ghost from the corner and lifted it up.

"Oh dear," Liu Ruyan said, watching with an expression that