Write as a chemical equations and balance
aluminum bromide and chlorine form and aluminum chloride and bromine

Try to write your equation. We'll tell you whether you're on the right path or not.

Al2Br+Cl2=AlCl+Br2

Actually, it's Al2Br6 + Cl2. Remember that Al is always trivalent. Bromide and chloride are, of course, monovalent. You can Google these if you don't know.

http://www.lmgtfy.com/?q=aluminum+bromide&l=1

Al2Br_6 + Cl_2 \rightarrow AlCl3 + Br_2


Check the aluminums. If you have more on the left, multiply the Al component on the Right by some small number.
Check the bromines. Again multiply the Br component on the right. You've already balanced Al on the left so if you decide to multiply Al2Br6, you'll also have to change the right side.
Do the same with chlorines.