Use the "toy model" reported in the $1999$ Physics Today article to solve d and G as functions of X$,$N and composition $($f$)$ for hexagonally$-$packed cylinders$($HEX$)$ and body centered cubic$($BCC$)$ spheres. Hint: derive the volume fraction dependance of the interfacial area per chain. Answer is d$=$X$^1/6$N$^2/3$f$^$a where a$=0($LAM$),1/6($cylinders$),2/9($spheres$)$