You must first get a common denominator by multiplying (1/3) by 5 and (-2/5) by 3 to get the equation (5/15)+(-10/15)= -5/15 which can be simplified to 1/3.
Covalent compounds share with each other, whilst Ionic compounds take from each other.
Covalent compounds are composed of 2 or more NONMETALS.
So, it would be CO, since the rest of the compounds contain metals in them.