Task: Question Answering
Input (English): Question: At a certain restaurant, the average (arithmetic mean) number of customers served for the past x days was 80. If the restaurant serves 120 customers today, raising the average to 90 customers per day, what is the value of x?

 Option A: 2

 Option B: 3

 Option C: 9

 Option D: 15

 Option E: 30
Output (English): Option B