A manufacturing company has a small production line dedicated to making a particular product. The line has four stations in serial. Inputs arrive at station $1$ and the output from station $1$ becomes the input to station $2.$ The output from station $2$ is the input to station $3$ and so on$.$ The output from station $4$ is the finished product. Station $1$ can process $2,700$ units per month, station $2$ can process $2,200/$month$,$ station $3$ can process $2,000/$month$,$ and station $4$ can process $2,100/$month$.$

a$.$ What station sets the maximum possible output from this system?