What is the highest common algebraic factor of the terms $8a$8a and $9a$9a?

What is the highest common algebraic factor of the terms $9ax$9ax and $8ba$8ba?

What is the highest common algebraic factor of the terms $6b^2y$6b2y and $11b^2a$11b2a?

What is the highest common algebraic factor of the terms $11n^2mb$11n2mb and $13xn^2y$13xn2y?