Admission to the state fair is $12, and each ride ticket costs $3.50. Write an expression to represent the situation and explain what the variable means.

3.50t + 12 where t represents the number of ride tickets
3.50a + 12 where a represents the cost of admission
12a + 3.50 where a represents the cost of admission
12t + 3.50 where t represents the number of ride tickets