Each of the main courses has a probability of being chosen. Each of the sweets has a chance of being chosen. And each of the drinks has a chance of being chosen too. So all possible combinations of meals have chance of being chosen.
(a) Chance of getting chicken: 1/3, chance of getting apple pie: 1/2, chance of getting coffee: 1/2. So the total chance is the product of the individual probabilities.
Repeat with the rest