I would say the answer is the first option. Usually when it asks for opposites, it wants something like the opposite of 15 is -15. Putting a negative on the outside means you solve the same, but you just add a negative sign on the number,
If I am rolling a single dice what is the probability of rolling a number that is divisible by 2 and 3? The only number divisible by 2 and 3 is 6. So, would the answer be 1 out 6 or 1/6