Find the number of solutions to a + 2b + 3c = 6 in nonnegative integers.
a b c
1 = (6, 0, 0) 2 = (4, 1, 0) 3 = (2, 2, 0) 4 = (0, 3, 0) 5 = (3, 0, 1) 6 = (1, 1, 1) 7 = (0, 0, 2)
