Answer
$W_{combined}=1991.43N$
Work Step by Step
First we find the mass of water:
$m= (1000 \frac{kg}{m^3})*(0.2m^3)$
$m=200kg$
Then the total mass of the system is:
$m_{total}=m_{plastic}+m_{water}=3kg+200kg=203kg$
And the weight of the combined system:
$W_{combined}=m_{total}g=(203kg)*(9.81\frac{m}{s^2})$
$W_{combined}=1991.43N$
