How would you balance this redox reaction by oxidation number method?

Question

C + O2 = CO2

Answer 1

C + O2 = CO2
C changes from zero on the left to 4+ on the right. A loss of 4e.
2 O changes from zero on the left to 4- on the right. A gain of 4e.
Yea! Loss of e = gain of e means it is balanced.