Copper : Aluminum = 7 : 4. Let Copper and Aluminum in the weapon be 7x and 4x respectively. Given, Aluminum in weapon = 12 kg So, 4x = 12, x = 3 Copper = 7x = 7 × 3 = 21 Kg. Total alloy in the weapon = 12 + 21 = 33 kg But 12% alloy get destroyed in making the weapon, that is, 88% alloy is used in the weapon, so, 88 % alloy = 33 kg 100 % alloy = 37.5 kg