so the question is blank are compbinations of numbers and operations
the answer is a numberical expression or a closed phrase
open phrase=numbers operations and placeholders exg 3+x
closed phrase=numbers operations no placeholder exg 3+4
open sentence=numbers operations placeholder and relation symbol (=><) exg 3+x=8
closed senctance=number operations no placeholder and relation symbol exg
3+4=9
so it's a closed phrase
