We can use dimensional analysis to take the given quantity and convert it to the quantity of interest:
In words: We begin with 4.00 moles of aluminum oxide, and there are 4 moles of aluminum per 2 moles of aluminum oxide in the balanced reaction. Finally, each mole of aluminum weighs 26.9815 grams.
With symbols: 4.00 mol Al2O3 * 4 mol Al/2 mol Al2O3 * 26.9815 g Al / 1 mol Al
Cancel units: 4.00 mol Al2O3 * 4 mol Al/2 mol Al2O3 * 26.9815 g Al / 1 mol Al = 215.852 g Al
With 3 sig figs: 215 g Al