Greetings.....
21-y
would be your algebraic expression...
Note.....If your wondering why its not y-21 instead, read below for clarification...
Up above it stated Y is less than...
What are they saying.. well, there basically saying the algebra variable ( in other words, the letter y) is LESS THAN 21.
Since its LESS than 21....221 is GREATER... So...
can you subtract y from 21 if its less?
NO
Can you subtract 21 from Y because y is less?
YES!
Hope this made sense!
~Queen Hanaenae