LCM( 75, 90 ) = 450
The formula for finding LCM is
$$ \text{LCM} (a, b) = \frac{ a \cdot b }{ \text{GCD}(a,b)} $$In this example we have: a = 75, b = 90 and GCD(75, 90) = 15.
$$ \text{LCM} (75, 90) = \frac{ 75 \cdot 90 }{ \text{GCD}(75,90)} = \frac{ 6750 }{ 15 } = 450 $$