What a strange question!
x is the variable you previously defined, so x*2 multiply the content of the variable by 2.
'x' is a char vector that happens to contain the same letter that you used to name a variable but that's totally irrelevant. 'x'*2 multiply the character codes of the char vector by 2. The character code of the 'x' character is 120, so you get 240.
See for example:
>> 'hello'*2
ans =
208 202 216 216 222
because the character codes of 'h' is 104, 'e' is 101, 'l' is 108 and 'o' is 111.
