LCM( 15, 30 ) = 30
The formula for finding LCM is
$$ \text{LCM} (a, b) = \frac{ a \cdot b }{ \text{GCD}(a,b)} $$In this example we have: a = 15, b = 30 and GCD(15, 30) = 15.
$$ \text{LCM} (15, 30) = \frac{ 15 \cdot 30 }{ \text{GCD}(15,30)} = \frac{ 450 }{ 15 } = 30 $$