Why can't we find the density and molarity given the masses of solute/solvent and molar masses?

From [2013 ACS Local Exam](https://www.acs.org/content/dam/acsorg/education/students/highschool/olympiad/pastexams/2013-olympiad-exam.pdf):


We have a $\ce{KNO3}$ solution prepared in water, and we know the masses of solute and solvent as well as the molar masses. I know that we can easily find molality, but how come density and molarity cannot be determined?


Since the solvent is water, can't the mass be converted to volume to find both values?


