Explanation:
once the level of medicine reaches a value, where 30% are 23mL (so, whatever is lost, is immediately replaced again), that is then the long run value for the amount of the drug in the patient's body.
so,
30% = 23 mL
1% = 30%/30 = 23/30 = 0.766666666...
100% = 1%×100 = 0.766666666... × 100 = 76.666666...
so, once the level reaches 76.666666... mL in the body, it will remain constant, as the daily filtered out 30% are 23 mL, and the daily add-on is also 23 mL.
so, the answer is
76.667 mL