now if you put them into actual boxes and number each you get the same answer as above, however no one has accounted for the boxes that aren't full
which would include 4 for each of the boxes that have only 1 blue crayon in it
and another 5 which only have 2 blue crayons in it.
all combinations would be if you make b1, b2, b3, b4 each of the blue crayons
and r1, r2, r3 each of the red crayons:
non full boxes:
b1
b2
b3
b4
b1, b2
b1, b3
b1, b4
b2, b3
b2, b4
= 9 boxes total non full with at least 1 blue crayon
full boxes:
(ALL BLUE)
b1, b2, b3
b1, b2, b4
b2, b3, b4
b1, b3, b4
= 4 boxes total full with 3 blue crayons
(1 BLUE, 2 REDS)
b1, r1, r2
b2, r1, r2
b3, r1, r2
b4, r1, r2
b1, r1, r3
b2, r1, r3
b3, r1, r3
b4, r1, r3
b1, r2, r3
b2, r2, r3
b3, r2, r3
b4, r2, r3
= 12 boxes total full with 1 blue and 2 red crayons
(2 BLUE, 1 RED):
b1, b2, r1
b1, b2, r2
b1, b2, r3
b1, b3, r1
b1, b3, r2
b1, b3, r3
b1, b4, r1
b1, b4, r2
b1, b4, r3
b2, b3, r1
b2, b3, r2
b2, b3, r3
b2, b4, r1
b2, b4, r2
b2, b4, r3
b3, b4, r1
b3, b4, r2
b3, b4, r3
= 18 boxes total full with 2 blue and 1 red crayons
OVERALL TOTAL of 34(full boxes) = (7C3) + 9 (non full boxes) == 43 BOXES with at least 1 BLUE CRAYON in it.