A rigid tank of volume 50 m³ contains a pure substance as a saturated liquid-vapour mixture at 400 kPa. Of the total mass of the mixture, 20% mass is liquid and 80% mass is vapour. Properties at 400 kPa are: \( T_{\text{sat}} = 143.61 \, \text{°C}, \, v_f = 0.001084 \, \text{m³/kg}, \, v_g = 0.46242 \, \text{m³/kg} \). The total mass of liquid-vapour mixture in the tank is \(\underline{\hspace{1cm}}\) kg (round off to the nearest integer).