In an experiment, 4 liters of water was observed to evaporate in 20 hours. what rate of evaporation was observed in this experiment?

The  Rate of Evaporation of water  is the rate at which water evaporates per unit time. It is measured  in liters per hour. Following is the how the calculation is done for this question:
Volume of water = 4 liters
Time taken to evaporate  =  20 hours
Therefore, Rate of evaporation = Volume of water  /  Time taken to evaporate
                                                  = 4 / 20
                                                  = 0.2 litres/ hour