Gabriella is organizing textbooks on her bookshelf. She has a Spanish textbook, a biology textbook, a history textbook, and a writing textbook. How many different ways can she line the textbooks up on her bookshelf?

Answer:
24
Step-by-step explanation:
We call:
A - Spanish textbook
B - Biology t.b.
C - Histoey t.b.
D - Writing t.b.
U can have:
ABCD
ABDC
ACDB
ACBD
ADBC
ADCB
BACD
BADC
BCDA
BCAD
BDAC
BDCA
etc..
U have 6 for each letter.
6×4=24