(a) One unit rate: 3 pieces of dark chocolate for each 1 piece of milk chocolate
Another unit rate: 6 pieces of dark chocolate for each 2 pieces of milk chocolate
(b) To find out how many pieces of milk chocolate are needed if 42 pieces of dark chocolate are used, we can set up a proportion using the given ratio:
36 dark chocolate / 12 milk chocolate = 42 dark chocolate / x milk chocolate
Cross multiplying, we get:
36x = 12 * 42
Simplifying,
36x = 504
Dividing both sides by 36,
x = 504 / 36
x = 14
Therefore, 14 pieces of milk chocolate are needed if 42 pieces of dark chocolate are used.