The answer is Conocen al vendedor viejo
In English, the verb Know is used for both Knowing a person or place, and Knowing something, when we talk about knowledge. But in Spanish, there is a different verb for each one of these uses. So, when we talk about knowing someone or someplace, we use the verb "Conocer". But when we talk about knowing something, like a fact, or a piece of information, or an answer, we use the verb "Saber". In this case, the phrase "They know the old salesman", is clearly referring to knowing a person, so to convey this in spanish, we use the verb "Conocer" conjugated in the 3rd person plural form "Ellos" or They.
i dont know what the answer is because i cannot see the question. if you take a better picture of it then i will let you know.