$7.$ In a steady$-$state reactive system, NaCl and H$2$CO$3$ are supplied to the system at the rate of $200$ L$/$min and $100$ L$/$min respectively, what is the rate at which Na$2$CO$3$ is produced?

a$)100$ L$/$min

b$)200$ L$/$min

c$)300$ L$/$min

d$)400$ L$/$min