Dimitrius returned 5 library books last week, returned 3 books this week and then checked out 8 more books. He now has 12 library books. How many books did he have before last week?

You need to change the English sentence into a math sentence (equation).

Dimitrius returned 5 library books last week, returned 5 => -5

returned 3 books this week Returned 3 => -3

and then checked out 8 more books. checked out 8 => +8

He now has 12 library books. Now has 12 => 12

How many books did he have before last week? the unknown call it B for books

B -5 -3 +8 = 12

can you solve that?