Each of the capital letters are substituted by a different digit from 0 to 9 in this 3x3 square such that the six sums formed by the leftmost column, rightmost column, top row, bottom row and the two main diagonals are each equal to x. Each of the remaining row and the remaining column may or may not sum to x.

A    B    C
D    E    F
G    H    I

Determine the respective minimum value and the maximum value of x.