Welcome to the forums.

This is a uniform distribution so there is an equal chance that (x) will be near any value from 0 to 1 as it will any other.

This is because it's distribution function is constant.

So if you are looking for the probability that (x) lies between b and a where a > b then it is just the difference between b and a

P{b < (x) < a} = a - b

You should check this out yourself look up uniform distribution in your text or on google. its a fairly simble derevation.

Now I am not sure if I am interpreting your question correctly, because it seems like a weird question to me... but that is how i would answer.

for the other P{a < (x) < 3b} = 3b - a