Final answer:
The condensed form of the given expression, 9z+9z, is 18z.
Step-by-step explanation:
The condensed form of the given expression, 9z+9z, is 18z. This can be obtained by combining the like terms, which in this case are the two terms with the variable z. Since they have the same coefficient of 9, we can simply add them together to get the result.