Explanation:
density = mass / volume
96.4 g of aluminum / volume = 2.7
therefore,
96.4 = 2.7 × volume
volume = 96.4 / 2.7 = 35.7037037... ml
back to iron :
7.87 = mass / 35.7037037...
mass = 7.87 × 35.7037037... = 280.9881481... g
it would be 280.9881481... g of iron in the same volume.