Please explain to the attached question step by step

Solve and show step by step, please Consider flipping two fair m-sided dice where X= sum and P(x)= m-| x-(m+1)| m2 , x = 2, ..., 2m Show/disprove: - p(x) is a valid pmf (p(x) 2 0, and E p(x) =1) - E(X) = (m+1)