Theo solved n + 5 = 11 for the unknown. The steps he took are shown.

He started with 5 tiles.

5 tiles.

Then he added tiles as he counted up to 11.

6 tiles.

He realized he added 6 more tiles to his original 5 to make 11. So he found the unknown to be 6.

How could Theo check his work? Check all that apply.

He could substitute 5 for n in the original equation and add.
He could substitute 6 for n in the original equation and add.
He could subtract 5 from 11 and check that the answer is 6.
He could subtract 11 from 5 and check that the answer is 6.
He could put all the tiles in 1 pile to count them to see if there are 11 in all.