Start by balancing elements that don’t appear in single form. So, for number 4
Start by adding 2 to Cu2O to balance the oxygen
2Cu2O + C —-> Cu + CO2
Now the oxygen is balanced, but the Cu is not. This can now simply be mitigated by adding 2 to the single Cu
2Cu2O + C —-> 2Cu + CO2
That’s your final answer for #4
