Final answer:
The inequality that describes how many stops Julia can afford given her budget and the price structure of the train ticket is 5 + 2.75 × S ≤ 21, representing the initial fee plus the cost per stop being less than or equal to her $21 budget.
Step-by-step explanation:
The scenario presented is a mathematical problem involving linear inequalities. Julia wishes to know the largest number of stops she can afford for a train journey given her budget of $21. The cost of the ticket is composed of an initial fixed fee of $5 with an additional fee of $2.75 for each stop. To represent this mathematically, let S be the number of stops, then the total cost is the sum of the initial fee plus the product of $2.75 and S. Thus, the inequality that describes Julia's situation would be the total cost being less than or equal to her budget, which is represented as 5 + 2.75 × S ≤ 21. This inequality checks for the maximum value of S that will not exceed Julia's budget.