Original volume = 20 × 15 × 12 = 3600 cm&sup3;.<br><br>New height = 12 × 1.25 = 15 cm.<br>New length = 20 × 0.80 = 16 cm.<br>Width unchanged = 15 cm.<br><br>&bull; New volume = 16 × 15 × 15 = 3600 cm&sup3;.<br><br>Final Answer: 3600 cm&sup3;