Using the grid technique, determine the least$-$cost location for the following problems.

$($a$)$ Location of the distribution facility between sources and markets.

$($b$)$ Location of distribution center to serve several customers. $($c$)$ For each of the above parts, see if you can visually demonstrate the approximate location of the supply and demand nodes, as well as the grid center you determined. You can use circles to represent the supply and demand nodes, where the diameter represents the approximate volume of the supply $($or demand$).$ Use a different symbol $($such as a $"*")$ for the least$-$cost location.