At the AoPS office, mice vary inversely with cats, that is, $\text{mice}=\frac{k}{\text{cats}}$, for some value of $k$. When there are $3r-19$ cats, there are $2r+1$ mice, and when there are $6r-24$ mice, there are $r-3$ cats. Find $k$.
Already posted: https://web2.0calc.com/questions/confusing-algebra
