LCM( 20, 144 ) = 720
The formula for finding LCM is
$$ \text{LCM} (a, b) = \frac{ a \cdot b }{ \text{GCD}(a,b)} $$In this example we have: a = 20, b = 144 and GCD(20, 144) = 4.
$$ \text{LCM} (20, 144) = \frac{ 20 \cdot 144 }{ \text{GCD}(20,144)} = \frac{ 2880 }{ 4 } = 720 $$