Answer:
In mathematics, it's a variable.
Step-by-step explanation:
In mathematics, it's a variable that could stand for a number. It's normally used in Pre-Algebra and up.
For example, if you say 5 + x = 15, you solve for x:
15 - 5 = x
10 = x
So plug the number in: 5 + 10 = 15.
Hope this helps!
