There are 4 periods in each working day of a school

There are 4 periods in each working day of a school. In how many ways can one organize 3 subjects such that each subject is allowed at least one period?

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 #43698