The GCD of n and 216 is 24 and their LCM is 864. Find n.
Use the fact that $\gcd(a,b)lcm(a,b)=ab$. So $\gcd(n,216)lcm(n,216)=216n=24\cdot 864$. So $n=\frac{24\cdot 864}{216}$.
+605 
