To determine the relative frequency that a student chose to wear both a white shirt and tan pants to the school function, we would need data on the total number of students and the number of students who wore both a white shirt and tan pants.
Since you haven't provided specific numbers or context, it's not possible for me to calculate this directly. However, if you're stating the percentages as options (20%, 25%, 35%, 65%), one of these options would correspond to the relative frequency; you would need to compare the relevant data about the students' clothing choices to find the correct answer.
If you have the data, please share it so I can assist you in determining the relative frequency!