-3x A 9x B 5x C
-9x A B C 8x D -4x E
5x F -7x G
1x F G 4x H -4x I
1x A B C D E -1x F G H I
Sol: A = 8; B = 1; C = 3; D = 20; E = 13; F = 7; G = 5; H = 15; I = 18