Question $3$

A construction company is currently undertaking $4$ construction projects at different locations, each project requires a certain amount of rebar per month. The company can purchase rebar from three suppliers, each with a different maximum monthly capacity. The transportation costs, supply, and demand are presented in the following table:

$\backslash$table$[[,$Project,$],[$Supplier$,$P$1,$P$2,$P$3,$P$4,\backslash$table$[[$Supply$],[($Ton$)]]],[$S$1,8,6,10,9,350],[$S$2,9,12,13,7,500],[$S$3,14,9,16,5,400],[$Demand $($Ton$),400,150,320,300,]]$

Determine the optimum monthly purchasing plan that would minimize the transportation costs using the North West corner method.