Answer of 24 gms seems to be correct. If some one says it not right, then he/she is probably wrong.
4 Al + 3 O₂ ==> 2 Al₂ O₃
Atomic weight of Aluminum = 27
Atomic weight of Oxygen = 16
So 108 gms of Aluminum reacts with 96 grams of Oxygen to completely burn and become an oxide.
Hence, 27 grams of Aluminum reacts with 24 grams of Oxygen.
4 moles of Al reacts with 3 moles of Oxygen. Or, One mole of Al reacts with 0.75 mole of Oxygen.