Density = mass/volume
If you have the density and volume of a substance, you can use this relationship to calculate the mass. Here, you have 149 milliliters of ethanol, and there are 0.789 grams of ethanol in every milliliter of ethanol. So the mass of 149 mL of ethanol can be obtained by multiplying: (0.789 g/mL)(149 mL) = 118 grams of ethanol.
