It’s 21 to 3 (Official clock system).

02:39

It’s 21 to 3.

Correct answer

02:40

It’s 20 to 3.

Error: 1 minute later

01:53

It’s 7 to 2.

Error: read minutes starting from hour markings and adding minutes

08:10

It’s 10 past 8.

Error: confuse hour and minute hands