GMAT Quantitative Reasoning Practice Test 1

To solve the problem, you need to add $\frac{4}{9}$ and $\frac{2}{3}$ then subtract $\frac{8}{18}$ since the amount she has not used is $\frac{8}{18}$, which reduces to $\frac{4}{9}$. If you were to add $\frac{4}{9}$ and $\frac{2}{3}$, and then subtract $\frac{4}{9}$, you would end up with $\frac{2}{3}$.