A company has two factories $${S_1},$$ $${S_2}$$ and two warehouses $${D_1},$$ $${D_2}$$ . the supplies from $${S_1}$$ and $${S_2}$$ are $$50$$ and $$40$$ units respectively. Warehouse $${D_1},$$ requires a minimum of $$20$$ units and a maximum of $$40$$ units. Warehouse $${D_2},$$ requires a minimum of $$20$$ units and, over and above, it can take as much as can be supplied. A balanced transport-ation problem is to be formulated for the above situation. The number of supply points, the number of demand points, and the total supply (or total demand) in the balanced transportation problem respectively are

The supply at three sources is $$50, 40$$ and $$60$$ units respectively whilst the demand at the four destinations is $$20, 30, 10$$ and $$50$$ units. In solving this transportation problem