ANSWER
842 boxes
Step-by-step explanation
In the morning, they unpacked 479 books.
In the afternoon, they unpacked 363 books.
To find out how many books were unpacked that day, we have to add the numbers that were unpacked in the morning and afternoon.
To solve the problem, we have to simply add, and we start by adding on the UNIT place value:
H T U
4 7 9
+3 6 3
8 4 2
That day, they unpacked 842 boxes.