For breakfast, the family decides to spend no more than $20.00 for the week.
Each day, the family drinks 2/7 of a liter of milk for breakfast.
For the entire week, the amount of milk consumed is

Milk costs $4,49 per liter, so the cost of the total amount of milk consumed is

So, the amount left for the granola is

Each day, the family eats 1/3 of a pound of granola for breakfast.
For the entire week, the amount of granola consumed is

Let x be the price per pound of the most expensive granola they can afford.

Therefore, the most expensive granola they can afford is $4.72