The inequality begins with the flat fee of $25. We then add the $13 per day for insurance as 13d, where d is the number of days. This gives us the expression
25 + 13d. Since he only has $121, we must use less than or equal to for our inequality; he can't spend any more than $121, but he can spend any number below it up to that number. This gives us
25 + 13d ≤ 121
