In a transportation problem with three locations and two destinations, the objective function is as follows: Min 20X11 + 18X21 + 23 X31 + 16X12 + 14X22 + 12X32. How much does it cost to ship one unit from location 2 to destination 1?
A. 18
B. 12
C. 23
D. 16
E. None of the above.