The least common multiple (LCM) of three numbers is the smallest number that is divisible by all three numbers. To find the LCM of 56, 63, and 84, we can list the multiples of each number and find the smallest number that appears in all three lists. The multiples of 56 are 56, 112, 168, 224, 280, 336, 392, 448, 504, 560, 616, 672, 728, 784, 840, 896, 952, 1008, 1064, 1120. The multiples of 63 are 63, 126, 189, 252, 315, 378, 441, 504, 567, 630, 693, 756, 819, 882, 945, 1008. The multiples of 84 are 84, 168, 252, 336, 420, 504, 588, 672, 756, 840, 924, 1008. The smallest number that appears in all three lists is 504, so the LCM of 56, 63, and 84 is 504.