Question 2
Natural numbers $a , b , c$ satisfy $\operatorname{gcd} \left(a , b\right) = 30 , \operatorname{lcm} \left(a , b\right) = 180 , \operatorname{gcd} \left(a , b , c\right) = 15$ and $\operatorname{lcm} \left(a , b , c\right) = 900$. Minimize $a + b + c$.