If the height is reduced by 3cm and becomes a cube, the surface area will be reduced by four equal small side areas (* * * 96cm2).

Reduced small side area =96÷4=24 square centimeters.

Cube side length =24÷3=8 cm

Original cuboid volume =8×8×(8+3)=704 cubic centimeters?

It is easier to understand by drawing a picture. It took some time to draw a picture, hehe.