LCM( 6, 15 ) = 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 = 6, b = 15 and GCD(6, 15) = 3.
$$ \text{LCM} (6, 15) = \frac{ 6 \cdot 15 }{ \text{GCD}(6,15)} = \frac{ 90 }{ 3 } = 30 $$