Final answer:
Tim can buy 20 cases of seltzer water with his entire $80 budget.
Step-by-step explanation:
To determine how many cases of seltzer water Tim can buy with his $80 budget, we need to divide his budget by the price of a case of seltzer water. Since a case of seltzer water costs $4, the calculation would be: $80 / $4 = 20. Therefore, Tim can buy 20 cases of seltzer water with his entire budget.