Translation:How much is it?
It is optional. Originally, question marks were not part of the Japanese writing style (at least says so Wikipedia: "疑問符は元来の日本語の書法にはない"¹). "However, the question mark is very commonly used, especially in casual and creative writing and in manga."² I'd say Western influence changed the writing style. Now it's very common³. However, it is not usually used in formal Japanese¹¹.