use conversion from g to kg
[tex]1\operatorname{kg}=1000g[/tex]convert the 420g
[tex]420g\cdot\frac{1\operatorname{kg}}{1000g}=0.420\operatorname{kg}[/tex]substract from the 1.5kg
[tex]1.5\operatorname{kg}-0.420\operatorname{kg}=1.08\operatorname{kg}[/tex]there are 1.08kg of soil left.
