You will need: (2240/625)*250=896 ml of treatment liquid. If each bottle contains 250 ml you'll need 3.6 bottles (3 bottles and a bit more than half a bottle).
I do not think you need the conversion 1 cubic meter=1000 litres unless the volume of the tank is in cubic meters BUT 2240 cubic meters seems too large!
2 is the coefficient because the coefficient always comes before the variable. In this case the variable is X, and 2 comes right before that signaling that it is (2)(x).
