The percentage $50\%$ is equivalent to the fraction $\frac{1}{2}$, while $75\%$ is equivalent to $\frac{3}{4}$. Since $50\%$ of $N$ is 16, then $\frac{1}{2}N=16$ or $N=32$. Therefore, $75\%$ of $N$ is $\frac{3}{4}N$ or $\frac{3}{4}(32)$, which equals 24.