A bucket that is $\frac{2}{3}$ full contains $9 \mathrm{~L}$ of maple syrup. What is the capacity of the bucket, in litres?
Since the bucket is $\frac{2}{3}$ full and contains $9 \mathrm{~L}$ of maple syrup, then if it were $\frac{1}{3}$ full, it would contain $\frac{1}{2}(9 \mathrm{~L})=4.5 \mathrm{~L}$.

Therefore, the capacity of the full bucket is $3 \cdot(4.5 \mathrm{~L})=13.5 \mathrm{~L}$.

ANSWER: $13.5 \mathrm{~L}$