Candies were sold in containers containing $3$ flavours: strawberry, chocolate and mint. The amount of mint candies to chocolate candies always stayed the same. The fraction of strawberry candies in $3$ different sized containers were $\frac{2}{5}$, $\frac{2}{7}$ and $\frac{2}{9}$. Given that the amount of mint candies always stayed the same as well and that the total mass of all $3$ containers is $1371\textasciitilde g$, determine the mass of all strawberry candies. 
Overseas Competition->Knowledge Point->Counting Modules->Inclusion-Exclusion Principle