To solve this question, we need to know the oxidation state of oxygen. It is -2.
Now we can calculate.
There are 2 atoms of Ec and 14 atoms of oxygen. We multiply the number of atoms for the oxidation state and sum, everything will equal to 0, because it is a neutral compound. As we don't know the oxidation state of Ec, let's put x in its place:
2x + 14(-2) = 0
2x = 14
x = +7
Answer: The oxidation state of Ec is +7.