Units of Concentration

A solution contains 30% w/w NH$_3$ (aq) (density: 0.90 g/mL). Find the mole fraction of the solution.

What is the mole percent and fraction of each component of a mixture composed of 0.200 mol O$_2$ and 0.500 mol N$_2$ ?

Calculate the mole fraction (and mole percent) of oxygen in exhaled air if the P$_{O_2}$ = 760 torr and P$_{total}$ is 1116 torr.