The LCM is 63
The common multiples of 9 and 21 are 63, 126, 189 and so on.
45 and 90
Any pair of numbers has an infinite set of common multiples. The lowest common multiple of 9 and 21 is 63 and the others are multiples of this, e.g. 63, 126, 189, 252, 315, ...
The gcf is 3
126
The LCM is 63.
63.
Their lowest common multiple is 63.
63
315
63, 126, 189
There is an infinite number of common multiples for 9 and 21. A common multiple of any two or more numbers is any number into which each of two or more numbers can be divided evenly (zero remainder).