Use the ten natural digits 0,1,2,3,4,5,6,7,8,9 each occurring only twice
and fill up the the 20 empty boxes in the figure shown below such that the resulting 13 numbers (7 vertical, 6 horizontal) are each multiple of 7 and their product is the highest of all such arrangements.
+---+
| |
+---+---+---+
| | | |
+---+---+---+---+---+
| | | | | |
+---+---+---+---+---+---+---+
| | | | | | | |
+---+---+---+---+---+---+---+
| | | | | |
+---+---+ +---+---+
Note: As the figure suggests, the bottom row should be considered as two 2-digit numbers rather than a single 4-digit number.
