If you were given a 16.0 ml sample of solution a, describe how you could determine the mass of the sample using only your graph answer

A density of the substance is an intrinsic property. Each substance has its own value of density, and it is constant. Since density is equal to mass over volume, a graph of mass vs volume would have a constant slope equal to density. So, it will be a linear graph. The mass is in the y-axis, and the volume is on the x-axis. Locate V = 16 mL on the x-axis, project it upwards until it intersects with the linear graph, then, move towards the left to determine the corresponding y-value, represented by the mass.

Yes she is correct. the answer is completely correct

You would do 1500/4 and the answer is 375