Aletter that represents an unknown number is

Hey there! Hello!

I believe what this question (more of a statement) is asking is to identify what a letter that represents an unknown number is called. Most of the time, i refer to it as just a variable, or an unknown variable. It can also be referred to as just an unknown value. 

Feel free to ask me any additional questions if you have any! :-)

The variable that's what it is called.. it could be represented with any letter but x most of the time

You're doing something i dont know how to do but search up on google slope calculator maybe that will get you there