Translation:How much should we tip?
给 needs to be the verb in Chinese because 小费 is a noun, not a verb. However, in English, tip can be its own verb or it can be a noun. In other words, 给 is needed in Chinese, but "give" is not needed in English. In my experience, "tip" as a verb is much more common than "tip" as a noun paired with the verb "give".