Answer is: She will need 6 aluminium and 9 oxygen atoms.
Substance made from aluminium and oxygen is aluminium oxide (Al₂O₃).
On molecule of aluminium oxide has two aluminium atomsa and three oxygen atoms.
So three molecules of aluminium oxide will have:
1) 3 · 2Al = 6Al; six aluminium atoms.
2) 3 · 3O = 9O; nine oxygen atoms.
