Write the following set in Roster form :

The set of letters in the word 'UNIVERSAL'.

Write the following set in Roster form :

A = {x : x = y + 3, y ∈ N and y > 3}.

Write the following set in Roster form :

C = { x : x is a composite number and 5 ≤ x ≤ 21 }

List the elements of the following set :

{ x : x² - 2x - 3 = 0 }