Final answer:
The yearly earnings of a student eligible for financial aid, represented by the variable s, must satisfy the inequality s ≤ $30,000.
Step-by-step explanation:
To determine the expression to represent the yearly earnings (in dollars) of a student eligible for financial aid, we use the variable s to denote these earnings. According to the requirements, a student must earn at most $30,000 a year to be eligible. Thus, the expression to represent the eligible earnings is s ≤ $30,000. In other words, any student whose earnings, s, are less than or equal to $30,000 would qualify for financial aid under this criterion.