Answer
36
Work Step by Step
Multiples of 12 : $12\times1, 12\times2, 12\times3, 12\times4, 12\times5, $
= 12, 24, 36, 48, 60
Multiples of 18 : $18\times1, 18\times2, 18\times3, 18\times4, 18\times5, $
= 18, 36, 54, 72, 90
Now 36 is the smallest common number in both the lists. so 36 is LCM of 12 & 18.