LCM( 15, 129 ) = 645
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 = 129 and GCD(15, 129) = 3.
$$ \text{LCM} (15, 129) = \frac{ 15 \cdot 129 }{ \text{GCD}(15,129)} = \frac{ 1935 }{ 3 } = 645 $$