Each of the capital letters in bold denotes a different base ten digit from 1 to 9 in this cryptarithmetic expression. It is known that A < B, D < E, G < H and, C < F < I

(A+B)*C + (D+E)*F + (G+H)*I

(I) Determine the respective smallest and the largest positive integer value that this expression can assume.

(II) Which positive integer value assumed by the above expression gives a unique solution?