O2 +2C=2CO
from equation for 1 molecule O2 is needed 2 molecules C, and we get 2 molecules of CO
ratio O2:2C=1:2
so for 60 atoms of carbon we need only 30 molecules of oxygen.
and from 60 atoms of carbon we get 60 molecules of CO, because from 2 atoms of C we get 2 molecules of CO