Finding the amounts of petrol
tank: $44$ litres $\frac14$ of $44 = 11$
$\frac13$ of $44 = 44\div3 = 14\frac23$
$\frac23$ of $44=44-14\frac23=29\frac13$
$29\frac13-11=18\frac13$
Finding the quantity as a fraction
The volume of petrol that Andrea put in is the difference between $\frac{2}{3}$ and $\frac{1}{4}$ of a tank.