To find the volume, just divide the mass by the dosage in mass per volume. Then, add both volumes to find the total volume. The solution is as follows:
45 mg ÷ 50 mg/mL = 0.9 mL
For the second unit, mcg is micrograms. For every 1 mcg, there is 0.001 mg. Thus,
400 mcg/ml * 0.001 mg/1 mcg = 0.4 mg/mL
0.3 mg ÷ 0.4 mg/mL = 0.75 mL
Total Volume = 0.9 mL + 0. 75 mL = 1.65 mL
