Hey there!
HCN + CuSO₄ → H₂SO₄ + Cu(CN)₂
Balance CN.
1 on the left, 2 on the right. Add a coefficient of 2 in front of HCN.
2HCN + CuSO₄ → H₂SO₄ + Cu(CN)₂
Balance H.
2 on the left, 2 on the right. Already balanced.
Balance SO₄.
1 on the left, 1 on the right. Already balanced.
Balance Cu.
1 on the left, 1 on the right. Already balanced.
Our final balanced equation:
2HCN + CuSO₄ → H₂SO₄ + Cu(CN)₂
Hope this helps!