A fishtank with inside dimensions of 65 cm X 45 cm X 80 cm is filled with water. What is the volume in cm3 of water required? What is the mass in grams of the water required? What is the mass in kilograms?

volume in cc = 65 cm x 45 cm x 80 cm = ?

Assuming the density of the water is 1.00 g/cc, then mass = volume x density
There are 1000 g in 1 kg.