Review how to calculate the mass of a liquid from its volume and density.

mass = volume x density

Density of liquids usually is expressed in units of g/ml. If you know the density of a liquid and the volume of the liquid, you can calculate its mass. Similarly, if you know the mass and volume of a liquid, you can calculate its density.

Calculate the mass of 30.0 ml of methanol, given the density of methanol is 0.790 g/ml

mass = volume x density

mass = 30 ml x 0.790 g/ml

mass = 23.7 g

In real life, you can usually look up the density of commons liquids in reference books or online.