Exercise-Manipulating an element in an array (Replace/Insert/Remove)

Given array sequence: S=(6, 5, 4, 3, 2, 1)

a) S.replaceElementAtRank(0,7)
(7, 5, 4, 3, 2, 1)

b) S.insertElementAtRank(1,7); S.replaceElementAtRank(3,8)
(6, 7, 5, 4, 3, 2, 1) => (6, 7, 5, 8, 3, 2, 1)

c) S.removeElementAtRank(2); S.insertElementAtRank(4,S.elementAtRank(2))
(6, 5, 3, 2, 1) => (6, 5, 3, 2, 3, 1)

d) S.insertElementAtRank(1,S.elementAtRank(2)); S.removeElementAtRank(S.elementAtRank(4))
(6, 4, 5, 4, 3, 2, 1) => (6, 4, 5, 3, 2, 1)