The solubility of potassium nitrate is $109\ \text{g}$ per $100\ \text{g}$ of water at $60\ ^\circ\text{C}$ and $32\ \text{g}$ at $20\ ^\circ\text{C}$. A saturated solution made with $50\ \text{g}$ of water at $60\ ^\circ\text{C}$ is cooled to $20\ ^\circ\text{C}$. What mass of crystals forms?