How do you write an algebraic expression for the phrase “a number subtracted from $18$”?

Hint: Algebraic operation or term for the phrase “subtracted from” is “-” that is subtraction operation and the phrase “a number” means it can be any digit or decimal or is generally say a real number so consider it as a variable. The term “subtracted from” means the number on the left side of the phrase is subtracted from the number on the right side of the phrase. Use this information to express the given phrase as an algebraic variable expression.

Complete step by step solution:
In order to express the phrase “a number subtracted from $18$”, as an algebraic variable expression, we should have the information about what types of algebraic operations are taking place in this phrase. From the given phrase “a number subtracted from $18$”
We can see that there is only one algebraic operation taking place, but what it actually means in algebraic significance.
Let us see what “subtracted from” means in terms of algebra
The phrase “a subtracted from b” represents the algebraic expression “$b - a$”
The first term “a number” can be any number belonging to the set of real numbers so we will take its value in an alphabet (say $x$) then we can easily express the given phrase. Therefore expression will be
 “a number subtracted from $18$”$ = 18 - x$

Therefore expression will be “a number subtracted from $18$”$ = 18 - x$

Note: Take care of the fact that commutative property does not hold good for subtraction so aware of the terms and signs you are writing in subtraction. Also if it was only written “a number” in place of “a number c”, then you yourself have to consider some variable in that place.