Given that the scale is 3 cm = 4 in
then
the side that is 8 inches long will now be
= 8/4 * 3 cm
= 2 * 3 cm
= 6 cm
the side 10 in will be
= 10/4 * 3 cm
= 7.5 cm
the side that is 16 in will be
= 16/4 * 3 cm
= 12 cm
the new sides are 6 cm, 7.5 cm and 12 cm