We have to calculate the dosis written by the doctor.
The order said 300 mg/kg daily.
The weight is 123 lb, so we have to convert it to kilograms (1 kg = 2.2 lb):
![W=123\text{ lb}\cdot\frac{1\operatorname{kg}}{2.2\text{ lb}}\approx56\operatorname{kg}]()
We then can calculate the dosis by multiplicating the dosis per kg times the weight:
![300\frac{mg}{\operatorname{kg}}\cdot56\operatorname{kg}=16800mg\cdot(1g)/(1000mg)=16.8g]()
The antibiotic dosis is 16.8 g/daily.