I am inputting a model into excel for the process flow diagram. This process has a sludge recycle. I want to be able to input a sludge recycle ratio that I can change which would update all the concentrations. I want to know what the equation is to solve for how much needs to be wasted to maintain a C$3$ of $30$ mg$/$L$.$ For the equation please write it using a recycle ratio. See attached PFD