Problem $2$: A new cellular service provider decided to employ a cluster of $19$ cells as the basic module for frequency reuse. Let us define the reuse distance as D and the cell radius as R$.$

$1.$ Can you identify one such cluster structure? $($The values of i and j$).$

$2.$ Can you get an alternate cluster structure for part $1.?$ If yes, what would change?

$3.$ Compute the reuse distance D for the system of part $1.,$ as a function of R$?$