a. LCD by inspection:
Write the multiples and take a consideration to 72,
6 = 0, 6, 12, 18, 24, 30, 36, 42, 48, 54, 60, 72, 78
18 = 0, 18, 36, 54, 72, 90
9 = 9, 18, 27, 36, 45, 54, 63, 72, 81
72 = 0, 72, 144,
So if we observe the lowest common multiple is 72.
b. LCD by division of prime numbers
Write the factors of the denominators 6, 18, 9, 72
6 = 2 x 3
18 = 2 x 3 x 3
9 = 3 x 3
72 = 2 x 2 x 2 x 3 x 3
The LCD = 2 x 2 x 2 x 3 x 3 = 72
