It’s 21 to 6 (Official clock system).

05:39

It’s 21 to 6.

Correct answer

05:40

It’s 20 to 6.

Error: 1 minute later

04:53

It’s 7 to 5.

Error: read minutes starting from hour markings and adding minutes

08:25

It’s 25 past 8.

Error: confuse hour and minute hands