Question

the mass of an Empty 40 litre petrol tank of vehicle 8kg what will its mass when completely filled with fuel of density 700 Kg 1 m cube

Answer 1

Fuel density = 700kg/m3 
volume = 40l = 0.04 m3
mass of fuel = 700 × 0.04 = 28kg

mass when filled = 8 + 28 = 36kg