We need to compute $\frac{2}{3} - \frac{1}{8}\text{.}$ The denominators are $3$ and $8\text{.}$ Notice that the denominator of $3$ is prime. So we can use that prime factor, as well as the prime factorization of $8\text{,}$ which is $2\cdot2\cdot2\text{,}$ to build our LCD. Thus, the least common denominator is $2\cdot2\cdot2\cdot3=24\text{.}$ So we need to rewrite each fraction using $24$ as the denominator: $$\begin{aligned} \frac{2}{3} - \frac{1}{8}\amp=\frac{2\cdot8}{3\cdot8} - \frac{1\cdot3}{8\cdot3}\\ \amp=\frac{16}{24}-\frac{3}{24}\\ \amp=\frac{13}{24} \end{aligned}$$ The numerical result is $\frac{13}{24}\text{,}$ but in order for this answer to make sense in the context of the problem being solved, we need to use the appropriate units. The amount of flour remaining is $\frac{13}{24}$ cups.