s1 help !!

I was doing a really old (2002) s1 paper and I came across a question I havent seen before, anyone know if this is still on the spec and please can someone explain it! Feel like I am missing something really obvious but I cant find any resources to help me, thanks!
4. A discrete random variable X takes only positive integer values. It has a cumulative distribution function F(x) = P (X ≤ x) defined in the table below.
X 1 2 3 4 5 6 7 8
F(x) 0.1 0.2 0.25 0.4 0.5 0.6 0.75 1
(a) Determine the probability function, P (X = x), of X.

Can't say whether it would be in the exam, but don't see why not.

Since the r.v. only takes positive integer values, then:

F(x) = F(x-1)+ P(X=x) for integer x, from the definition of the cdf.

Reassrange to make P(X=x) the subject and use the given data.