Final answer:
In terminal-digit filing, the first filing unit for a patient's chart number 345601 is 34.
Step-by-step explanation:
In terminal-digit filing, the patient's chart number is divided into three parts: the last two digits, the middle two digits, and the first two digits. The first filing unit is determined by the first two digits of the patient's chart number. In this case, since the patient's chart number is 345601, the first filing unit would be 34.