I would start with the SO4 on the reactant side. You have 3. That means that you need to put a coefficient of 3 in front of the product CaSO4 (remember that you can't change the subscripts, only the coefficients).
Now you have 3 Ca on the product side, so put a 3 in front of calcium hydroxide. Now your Ca and the SO4 are balanced.
Check how many Al you have on reactant side....put a 2 in front of aluminum hydroxide.
Last, check your hydroxide (OH) ions. 6 total on reactant side and 6 on product side.