6 friends are living in 6 different flats of an apartment

6 friends are living in 6 different flats of an apartment. Each of them was allotted a parking spot to park their cars in the ground floor. But they used to park their cars randomly in any of the 6 parking spots. In how many ways can they park their cars so that exactly 4 people park their cars in the spots allotted to them?

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 #10021