The concentration of volume of solution can be expressed in many ways for example: mass percent, volume percent, mass-by-volume percent, etc.
The formula for mass-by-volume percent is:
mass-by-volume percent =
2% erythromycin solution means 2 g of erythromycin in 100 mL.
Consider, for 15 g the volume be X mL.
So,
Hence, the volume is
.