For the first table, we notice that:
Therefore, the cost of the apples and the number of apples have a proportional relationship.
For the second table, we notice that:
Therefore, the cost of the pizza and the number of toppings are not proportional.
Answer:
(a) The cost of the apples is proportional to the weight of the apples.
(b) The cost of the pizza is not proportional to the number of toppings.
(c) Let p be the number of pounds, and c be the cost in dollars, then we can set the following equation: