The value of x is a constant number . The letter "x" is often used in algebra to mean a value that is not yet known. It is called a "variable" or sometimes an "unknown". so no one can decide the fix value of x because it ia a variable .
In x + 2 = 7, x is a variable, but we can work out its value if we try! A variable doesn't have to be "x", it could be "y", "w" or any letter, name or symbol.
