Answer: Depends.
Explanation:
You have two options for this question, either you can solicit opinions or offer an answer yourself. Considering the tone is formal, soliciting opinions would be best so people don't get angry about your answer. From researching online here are some of the possible answers:
The two numbers closest to 8.4 must be 9 and 7
The two numbers close to 8.4 could be 4 and 6 but really it depends on what you think makes sense when striving for equality with out specifying The fact that there is no exact answer here is one of the tips and tricks mathematics teaches us in life - sometimes we're dealing with approximation and not absolutes itself!