It’s 21 to 4 (Official clock system).

03:39

It’s 21 to 4.

Correct answer

03:40

It’s 20 to 4.

Error: 1 minute later

02:53

It’s 7 to 3.

Error: read minutes starting from hour markings and adding minutes

08:15

It’s a quarter past 8.

Error: confuse hour and minute hands