Answer:
A, C, and D
Step-by-step explanation:
A is one answer because if you were to add 3.9 and the value of ?, you would get 8.6. The same would apply to C, just backwards because it is 8.6 = 3.9 + ?. Finally, D is another answer because if you subtract 3.9 from 8.6, you will get the value of ?.
