Here the number of trucks is 4 and vacant spaces are 6. So the given assignment problem is the unbalanced problem. So we introduce two dummy columns with all the entries zero to make is balanced. So the problem is
Here only 4 vacant spaces can be assigned to four trucks
Step 1: Not necessary since all rows have zeros.
Step 2:
Step 3: (Assignment)
The optimal assignment schedule and total distance travelled is
Thus the minimum distance travelled is 12 km.