Explanation:
The volume of the rectangular fish tank is:
V = l x w x h = 60 cm x 15 cm x 34 cm = 30,600 cm³
Since the tank is 1/3 full, the volume of water in the tank is:
V_water = (1/3) x V = (1/3) x 30,600 cm³ = 10,200 cm³
To find the volume of water needed to fill the tank completely, we can subtract the volume of water already in the tank from the total volume of the tank:
V_needed = V - V_water = 30,600 cm³ - 10,200 cm³ = 20,400 cm³
Therefore, 20,400 cm³ of water is needed to fill the tank completely.