Let:
T = Total money they have
Dc = Dog collar
x = Number of bags of food

Let's solve the inequality:

This means that they can buy 12 bags of food at most.
Since they plan to buy 2 bags of food:

This means they can do it and have $ 11.5 to spare
Answer:
This is a linear function because the power of x is 1. Because of the +40 it's not a proportional relationship (they are in the form y = kx but the given equation is not) so the answer is the second option.
$50 corresponds to 4 kg
That means there must be a number that when you multiply by 4 you get 50.
Let that number be k. k is the price of cheese per kg.
1 kg: y = k * 1
2 kg: y = k * 2