(b) To find the number of different selections David can make, we consider the combinations of chocolates he can choose:

1. Choose 2 dark, 2 white, and 1 milk: \(\binom{6}{2} \times \binom{4}{2} \times \binom{1}{1} = 90\)
2. Choose 3 dark, 1 white, and 1 milk: \(\binom{6}{3} \times \binom{4}{1} \times \binom{1}{1} = 80\)
3. Choose 1 dark, 3 white, and 1 milk: \(\binom{6}{1} \times \binom{4}{3} \times \binom{1}{1} = 24\)

Summing these gives the total number of ways: \(90 + 80 + 24 = 194\).

(c) To find the number of different passwords Chelsea can make, we consider the combinations of characters:

1. Choose 2 capital letters, 1 digit, and 1 symbol: \(\binom{26}{2} \times 9 \times 5 \times 4! = 351,000\)
2. Choose 1 capital letter, 2 digits, and 1 symbol: \(26 \times \binom{9}{2} \times 5 \times 4! = 112,320\)
3. Choose 1 capital letter, 1 digit, and 2 symbols: \(26 \times 9 \times \binom{5}{2} \times 4! = 56,160\)

Summing these gives the total number of passwords: \(351,000 + 112,320 + 56,160 = 519,480\).