。
Mr. Hirayama is a very good teacher.
Literal
Hirayama-teacher [topic-は] very good teacher is.
大変 means 'very/extremely' — slightly more formal than とても. 良い先生 is 'a good teacher.' A simple compliment about someone's teaching. 先生 appears twice: once as an honorific suffix on the name and once as the predicate noun.