A sample of 26.4g of aluminum yields 260.8g of aluminum bromide.
It's obvious that the 260.8g of aluminium bromide formed contains 26.4g of Aluminum by composition (with reference to Law Of Mass Combination). By deducing the number of moles of Aluminium and Bromine from their respective mass combination, you can deduce the emperical formula of Aluminium Bromide.
How many grams of bromide react with 16.4g of aluminum?
Once you have derrived the emperial formula of aluminium bromide, you can deduce how many moles of bromine has reacted with the number of moles of aluminium equivalent to 16.4g