Factor the following expression: $28z^{97}+7z^{96}$.
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Factor the following expression: $28z^{97}+7z^{96}$.
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
7z^{96}(4z+1)
Factor the following expression: $28z^{97}+7z^{96}$.
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