jmc

By the definition of inverse proportion, the product $jk=C$ for some constant $C$. Substituting the given values, we can see that $16\cdot 21=336=C$. Using this $C$ value, we can solve for $j$ when $k=14$: $$\begin{array}{rl}j\cdot 14& =336\\ \Rightarrow j& =\frac{336}{14}=\boxed{24}\end{array}$$