A feed stream of pure liquid water enters an evaporator at a rate of 0.75 kg/s. Three streams come from the evaporator: a vapor stream and two liquid streams. The flow rate of the vapor stream was measured to be 6 x 106 L/min and its density was 2.5 g/m3. One of the liquid streams is discharged as waste, the other is sent on to another part of the plant at a rate of 17.5 kg/min. Calculate the flow rate of the waste discharge in kg/min.
p/s: I think have to use the mass balance - rate of change