LCM( 30, 42 ) = 210
The formula for finding LCM is
$$ \text{LCM} (a, b) = \frac{ a \cdot b }{ \text{GCD}(a,b)} $$In this example we have: a = 30, b = 42 and GCD(30, 42) = 6.
$$ \text{LCM} (30, 42) = \frac{ 30 \cdot 42 }{ \text{GCD}(30,42)} = \frac{ 1260 }{ 6 } = 210 $$