Let M be a 33 magic square with magic number s. (a) Prove that the sum of

Question:

Let M be a 3×3 magic square with magic number s.
(a) Prove that the sum of M's entries is 3s.
(b) Prove that s = 3 ∙ m2,2.
(c) Prove that m2,2 is the average of the entries in its row, its column, and in each diagonal.
(d) Prove that m2,2 is the median of M's entries.