Grid: 6, 0, 9, 3|9, 0, 12, 3|6, 3, 9, 6|9, 3, 12, 6|12, 3, 15, 6|0, 6, 3, 9|3, 6, 6, 9|6, 6, 9, 9|12, 6, 15, 9|0, 9, 3, 12|3, 9, 6, 12|6, 9, 9, 12|12, 9, 15, 12