What volume of ethanol $($density $=0\mathrm{.}7893\frac{g}{c}{m}^3)$ should be added to $450mL$ of water in order to have a solution that freezes at $-15\mathrm{.}0C?[$For water, $K_f=1\mathrm{.}86\frac{C}{m}.]$

What is the osmotic pressure of a solution that contains $13\mathrm{.}7g$ of propyl alcohol $(C_3{H}_{7}OH)$ dissolved in enough water to make $500mL$ of solution at $27C?$

A $0\mathrm{.}100m{K}_{2}S{O}_4$ solution has a freezing point of $-0\mathrm{.}43C.$ What is the van't Hoff factor for this solution? $K_f=1\mathrm{.}86\frac{C}{m}$