Answer:
HCN+CuSO4->H2SO4+Cu(CN)2
2,1,1,1
1.Add 2 to HCN it then becomes (H=2, C=2, N=2,) (had to add 2 cz on right side you had H2 in H2SO4)
2.1(nothing) cz on both sides we got 1Cu and 1SO4
3.1 cz again we have H2 on both sides and 1SO4 on both sides
4.1 cz we got 1Cu on both sides and 2C 2N on both sides (1st step)