I need to know the equation for The staff commute to work in different ways 2/5 drive, 4/15 catch the bus and 1/3 cycle order the fractions starting with the largest

The easiest way is to find a common denominator so that you can directly compare the numerators of the fractions. Here, notice that $3$ and $5$ both have $15$ in their multiplication table, so you can set all three denominators to $15$.

In order to set $\frac{2}{5} $ to denominator $15$, we have to multiply the denominator by $3$, but that means we also have to multiply the numerator by $3$ to keep the fraction equal.
So $\frac{2}{5}*\frac{3}{3} = \frac{6}{15} $ (notice that multiplying by $\frac{3}{3} $ we're essentially multiplying by $1$ so the value of the fraction doesn't change, we're just rescaling it to denominator $15$)

Now to set $\frac{1}{3}$ to denominator $15$, we can multiply the denominator and numerator by $5$ so we get $\frac{1}{3} * \frac{5}{5} = \frac{5}{15}$

So the three fractions to rank are $\frac{4}{15} $, $\frac{2}{5} = \frac{6}{15} $, $\frac{1}{3} = \frac{5}{15} $ 

Now by looking at the numerators when the denominators are equal, it is clear that the correct order from largest to smallest is $\frac{2}{5}, \frac{1}{3}, \frac{4}{15} $  

Hopefully that answers everything!