code: def num_plates_ET(q_plant, W_chan):
      
      num_plates = np.ceil(np.sqrt(q_plant / (design.ent_tank.CENTER_PLATE_DIST.magnitude
                                              * W_chan * design.ent_tank.CAPTURE_BOD_VEL.magnitude * np.sin(
                  design.ent_tank.PLATE_ANGLE.to(u.rad).magnitude))))
      return num_plates
docs: Return the number of plates in the entrance tank.
  
      This number minimizes the total length of the plate settler unit.
  
      Parameters
      ----------
      q_plant: float
          Plant flow rate
  
      W_chan: float
          Width of channel
  
      Returns
      -------
      float
          ?
  
      Examples
      --------
      >>> from aguaclara.play import*
      >>> num_plates_ET(20*u.L/u.s,2*u.m)
      1.0