al + cuso₄ → al₂(so₄)₃ + cu

Explanation:

Step1: Balance sulfate ions

There are 3 sulfate ions in $Al_2(SO_4)_3$. So we need 3 moles of $CuSO_4$. $Al + 3CuSO_4\rightarrow Al_2(SO_4)_3+Cu$

Step2: Balance aluminum atoms

There are 2 aluminum atoms in $Al_2(SO_4)_3$. So we need 2 moles of $Al$. $2Al + 3CuSO_4\rightarrow Al_2(SO_4)_3+Cu$

Step3: Balance copper atoms

There are 3 moles of copper in 3 moles of $CuSO_4$. So we need 3 moles of $Cu$. $2Al + 3CuSO_4\rightarrow Al_2(SO_4)_3+3Cu$

Answer:

$2Al + 3CuSO_4\rightarrow 1Al_2(SO_4)_3+3Cu$