Answer=4.5kg

Step-by-step explanation:

A solid rectangular 10 cm long 8 cm wide and 6cm

weight 9 kg

length is 20 cm with 4 cm and thickness 3cm

for solid

10×8×6=480cm³

480cm³=9kg

1cm³=9/480kg

for another solid

20×4×3=240cm³

240cm³=9/480kg

=9×240/480kg

=4.5kg