Thanks Alan 
6,9,20
Q=6a+9b+20c
(6a+9b+20c)modulo 6 = r
(9b+20c) modulo 6 =r
What numbers are possible if r=1
1x 7x 13x 19x 25x 31x 37x 43x 49=2*20+1*9 43 is the biggest that can not be packaged
What numbers are possible if r=2
2x 8x 14x 20=20*1 14 is the biggest but it is smaller than 43
What numbers are possible if r=3
3x 9=1*9 3 is the biggest but it is smaller than 43
What numbers are possible if r=4
4x 10x 16x 22x 28x 34x 40=2*20 34 is the biggest but it is smaller than 43
What numbers are possible if r=5
5x 11x 17x 23x 29=1*20+1*9 23 is the biggest but it is smaller than 43
so
43 is the biggest number that can not be packaged!
That is so snazzy