A real estate firm wishes to open four new offices in the Boston area. There are six potential sites available. Based on the number of employees in each office and the location of the properties that each employee will manage, the firm estimated the total travel time in hours per day for each office and each location. Find the optimal assignment of offices to sites to minimize employee travel time.

Offices A B C D 1 10 3 3 8 2 13 5 2 6 Sites 3 12 9 9 4 4 14 2 7 7 5 17 7 4 3 6 12 8 5 5