At a certain restaurant, the average (arithmetic mean) number of customers served…

At a certain restaurant, the average (arithmetic mean) number of customers served for the past x days was 85. If the restaurant serves 120 customers today, raising the average to 90 customers per day, what is the value of x?

This problem repeats another one in the library (at most with different numbers), so it's left out of browsing.

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #35022