Number 1 is x=8!!
2 is pretty confusing so I hope someone else can answer two as I have answered 1!
It would be 5.4 knowing that 9.6 is not the diameter you would need a larger radius so that when it is doubled you get a good number :)
While none of these examples can be used as an counterexample i could make one up to prove the conclusion is false. ex: 3-5=-2