Is that a sentence? Where is the verb? It certainly appears to be a sentence Fragement to me.
How do I fix this sentence? With five gallons of gas. They are asking for punctuating sentences.
To fix the first sentence and make it a complete sentence, you can add a verb. For example, you can rephrase it as "Is that a sentence? Where is the verb?" In this case, "is" is the verb.
As for the second sentence, "With five gallons of gas" is a prepositional phrase acting as an answer to the question. To make it a complete sentence, you can add a subject and a verb. For instance, you can write, "You can fix this sentence with five gallons of gas." In this case, "you" is the subject and "can fix" is the verb.
When punctuating sentences, it is important to ensure they are grammatically correct and convey a complete thought.