#### Answer

126

#### Work Step by Step

Multiples of 9 : 9,18,27,36,45,54,63,72,81,90,99,108,117,126.
Multiples of 14 : 14,28,42,56,70,84,98,112,126,140
Multiples of 21 : 21,42,63,84,105,126
Now 126 is the smallest common number in all the lists. so 126 is LCM 9, 14, 21.