The answer is (25hb^6) / (4z^6)
To get to this point, you first need to multiply 2h and 25b^6, Which leaves you with 50hb^6.
Next, you simplify by dividing 50 and 8 by the Greatest Common Factor, which in this case is 2. That leaves you with (25hb^6) / (4z^6).
Hope this helps!