If you understand the concept of human time, you can say that you can play the same instrument alone, so there are always 20+ 16+24=60 people who can play this instrument.

Starting from the electronic organ, there are 24 people who can play the electronic organ, so if 24 people are removed, there are still 36 people left.

There are 10 people who can play the piano and the electronic organ, so take out 10 people and there are 26 people left.

There are 8 people who can play accordion and electronic organ, so remove 8 people and leave 18 people.

This 18 person-time is the person-time who can play the piano and accordion, among which 8 people can play the accordion and piano, so if 8 people are removed, there are 10 people.

In this way, we have eliminated those who can play two instruments, and the rest are those who can only play one instrument.

There are 24 people who only know electronic organ, and 10 people who only know accordion and piano, making a total of 34 people. There are 38 people in total, and at least four people can't do anything without considering that someone knows three musical instruments.

I don't know if you understand, but if you don't, you can call me again. Good luck.