if i have something like
g/kg*year, can that be re written as g/kg/year?
if you have
$\displaystyle \frac{A}{BC}$
it is equal to
$\displaystyle \frac{\frac{A}{B}}{C}$ where B and C are interchangeable
if you have $\displaystyle \frac{A}{B}C=\frac{AC}{B}=\frac{C}{B}A$
it is NOT equal to
$\displaystyle \frac{\frac{A}{B}}{C}=\frac{\frac{A}{C}}{B}$